<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549


                                  SCHEDULE 13D

                    Under the Securities Exchange Act of 1934

                              (Amendment No. ___)*



                           priceline.com Incorporated
-------------------------------------------------------------------------------
                                (Name of Issuer)

                     common stock, par value $.008 per share
-------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                    741503106
-------------------------------------------------------------------------------
                                 (CUSIP Number)

                            Robert S. Harkey, Esquire
                     Senior Vice President - General Counsel
                              Delta Air Lines, Inc.
                    Hartsfield Atlanta International Airport
                             Atlanta, Georgia 30320
                                 (404) 715-2387
-------------------------------------------------------------------------------
      (Name, Address and Telephone Number of Person Authorized to Receive
                          Notices and Communications)

                                  July 11, 1999
-------------------------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)



If the filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of ss.ss.240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the
following box. [ ]

NOTE: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. See ss.240.13d-7(b) for other
parties to whom copies are to be sent.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).

                         (Continued on following pages)
                              (Page 1 of 13 pages)



<PAGE>   2



                                  SCHEDULE 13D

------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 2 of 13 Pages
------------------------                                -----------------------

-------------------------------------------------------------------------------
1         NAME OF REPORTING PERSON
          S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

          Delta Air Lines, Inc.


-------------------------------------------------------------------------------
2         CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*            (a) [ ]
                                                                       (b) [ ]


-------------------------------------------------------------------------------
3         SEC USE ONLY


-------------------------------------------------------------------------------
4         SOURCE OF FUNDS*

          OO

-------------------------------------------------------------------------------
5         CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEMS 2(d) or 2(e)                                               [ ]


-------------------------------------------------------------------------------
6         CITIZENSHIP OR PLACE OF ORGANIZATION

          Delaware
-------------------------------------------------------------------------------
                             7      SOLE VOTING POWER

          NUMBER OF                 9,309,701
           SHARES            --------------------------------------------------
        BENEFICIALLY         8      SHARED VOTING POWER
         OWNED BY
            EACH                    0
         REPORTING           --------------------------------------------------
          PERSON             9      SOLE DISPOSITIVE POWER
           WITH
                                    9,309,701
                             --------------------------------------------------
                            10     SHARED DISPOSITIVE POWER

                                    0
-------------------------------------------------------------------------------
11        AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

          9,309,701
-------------------------------------------------------------------------------
12        CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*
                                                                           [ ]

-------------------------------------------------------------------------------
13        PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

          6.1%
-------------------------------------------------------------------------------
14        TYPE OF REPORTING PERSON*

          CO
-------------------------------------------------------------------------------
                      *SEE INSTRUCTIONS BEFORE FILLING OUT!



<PAGE>   3

------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 3 of 13 Pages
------------------------                                -----------------------

ITEM 1            SECURITY AND ISSUER

                  This statement relates to the common stock, par value $0.008
per share, of priceline.com Incorporated, a Delaware corporation. The address of
the principal executive offices of priceline.com is Five High Ridge Park,
Stamford, Connecticut 06905.

ITEM 2            IDENTITY AND BACKGROUND

                  This statement is being filed by Delta Air Lines, Inc., a
Delaware corporation. The principal executive offices of Delta are located at
Hartsfield Atlanta International Airport, Atlanta, Georgia 30320.

                  Delta provides scheduled air transportation over an extensive
route network. Based on calendar 1998 data, Delta is the largest U.S. airline
in terms of aircraft departures and passengers enplaned, and the third largest
U.S. airline as measured by operating revenues and revenue passenger miles
flown. As of July 21, 1999, Delta provided scheduled air service to 142 cities
in 41 states, the District of Columbia, Puerto Rico and the U.S. Virgin
Islands, and to 42 international cities in 28 countries. In addition to
scheduled passenger service, Delta provides air freight, mail and related
aviation services.

                  The name, principal occupation and business address of each of
the directors and executive officers of Delta are set forth on Schedule A
hereto. Each director and executive officer of Delta is a citizen of the United
States of America. Neither Delta nor, to the best of its knowledge, any of its
directors or officers has during the last five years been (i) convicted in a
criminal proceeding (excluding minor traffic violations or similar misdemeanors)
or (ii) a party to a civil proceeding of a judicial or administrative body of
competent jurisdiction and as a result of such proceeding was or is subject to a
judgment, decree or final order enjoining future violations of, or prohibiting
or mandating activities subject to, federal or state securities laws or finding
any violation with respect to such laws.

ITEM 3            SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION

                  Delta holds a warrant, evidenced by a Participation Warrant
Agreement dated as of August 31, 1998, pursuant to which Delta has the right to
purchase 18,619,402 shares of priceline.com's common stock at an exercise price
of $0.9254896 per share. The warrant becomes exercisable on December 31, 2005,
but may become exercisable earlier, in whole or in part, upon the achievement of
performance thresholds relating to sales of Delta airline tickets through
priceline.com's internet-based buying service.

                  Delta has been notified that, as of July 11, 1999, based on
the achievement of certain performance thresholds, Delta's warrant became
exercisable with respect to 9,309,701 shares of priceline.com's common stock.
Under Rule 13d-3(d)(1), Delta is deemed to own

<PAGE>   4
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 4 of 13 Pages
------------------------                                -----------------------

beneficially all shares of priceline.com's common stock which Delta has the
right to acquire within 60 days. Accordingly, Delta is deemed to be the
beneficial owner, for purposes of Rule 13d-3(d)(1), of the 9,309,701 shares of
priceline.com's common stock for which Delta's warrant is currently exercisable.

                  Priceline.com offers tickets for sale on Delta pursuant to an
Airline Participation Agreement between Delta and priceline.com dated August 31,
1998. Delta acquired its warrant (on terms that were later amended) in
connection with its agreement to enter into the Airline Participation Agreement
and a related agreement. The terms of the Airline Participation Agreement and
the related agreement are described generally in Item 4 below.

                  One of the performance thresholds that Delta must meet in
order for its priceline.com warrant to become exercisable prior to December 31,
2005 is that a specified level of sales of Delta tickets through the
priceline.com service must satisfy a qualifying gross margin criterion. In July
1999, in connection with an amendment to the terms of the Airline participation
Agreement and the related agreement, priceline.com represented that all sales of
Delta tickets sold through the priceline.com service to date have met this
criterion.


ITEM 4            PURPOSE OF TRANSACTION

                  As discussed under Item 3 above, Delta acquired its warrant in
connection with its entering into an Airline Participation Agreement with
priceline.com on August 31, 1998. The Airline Participation Agreement nominally
has a ten-year term but is subject to termination by Delta after August 31, 2001
upon 180 days' notice to priceline.com. The Airline Participation Agreement does
not impose any material obligations on Delta. Delta is not obligated to supply
airline tickets to priceline.com and may supply airline tickets to
priceline.com's competitors at any time and at any price, without offering any
airline tickets to priceline.com. In addition to the Airline Participation
Agreement, priceline.com and Delta are parties to a related agreement which
provides, among other things, certain incentives designed to encourage Delta to
increase its participation in priceline.com's buying service. Under this
agreement, Delta is entitled to share in revenue generated from airline ticket
sales on Delta if priceline.com's gross margin on those sales exceeds
approximately 12% in any calendar quarter. In addition, priceline.com is
required to use the highest qualifying fare to fulfill ticket requests allocable
to Delta, subject to an agreed minimum ticket sale margin to priceline.com. The
agreement also requires priceline.com, subject to various exceptions, to obtain
Delta's approval of the addition of new carriers to the priceline.com service
and restricts the routes for which tickets may be offered by specified carriers
through the priceline.com service. Delta also may require the exclusion of
specific markets in order for certain other airlines to participate.
Priceline.com also is required to license its buyer-driven commerce system to
Delta on a non-exclusive basis and on commercially reasonable terms under
specified conditions. In addition, priceline.com's ability to transfer or
license its intellectual property to other travel providers is limited in the
manner set forth in the agreement.

                  Delta currently anticipates partially exercising its warrant
and selling up to approximately 1.8 million shares of priceline.com's common
stock as part of a proposed public offering by priceline.com of convertible
subordinated notes and common stock. Generally, Delta holds its warrant to
purchase priceline.com's common stock for investment purposes. Depending on
market conditions and other factors, including evaluation of priceline.com's
businesses and prospects, availability of funds, alternative uses of funds and
general economic conditions, Delta may from time to time further exercise its
warrant (to the extent that the warrant is then

<PAGE>   5
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 5 of 13 Pages
------------------------                                -----------------------

exercisable), hold the shares received upon exercise, acquire additional
securities of priceline.com or dispose of all or a portion of its investment in
priceline.com.

                  Except as described in this statement, neither Delta nor, to
the best of its knowledge, any of the persons named in Schedule A to this
statement presently has any plans or proposals which relate to or would result
in any of the following:

                  (a) The acquisition by any person of additional securities of
priceline.com, or the disposition of securities of priceline.com;

                  (b) An extraordinary corporate transaction, such as a merger,
reorganization or liquidation, involving priceline.com or any of its
subsidiaries;

                  (c) A sale or transfer of a material amount of assets of
priceline.com or any of its subsidiaries;

                  (d) Any change in the present board of directors or management
of priceline.com, including any plans or proposals to change the number or term
of directors or to fill any existing vacancies on the board;

                  (e) Any material change in the present capitalization or
dividend policy of priceline.com;

                  (f) Any other material change in priceline.com's business or
corporate structure;

                  (g) Changes in priceline.com's charter, bylaws or instruments
corresponding thereto or other actions which may impede the acquisition of
control of priceline.com by any person;

                  (h) Causing a class of securities of priceline.com to be
delisted from a national securities exchange or to cease to be authorized to be
quoted in an inter-dealer quotation system of a registered national securities
association;

                  (i) A class of equity securities of priceline.com becoming
eligible for termination of registration pursuant to Section 12(g)(4) of the
Act; or

                  (j) Any action similar to any of those enumerated above.

                  Delta is a party to a Registration Rights Agreement, dated as
of December 8, 1998, among priceline.com and some of priceline.com's
stockholders and warrantholders, pursuant to which the stockholders and
warrantholders have the right in certain circumstances to require priceline.com
to register their shares of common stock for resale under the Securities Act of
1933. Except in limited circumstances, priceline.com is obligated to pay all
expenses in connection with such a registration. A copy of the Registration
Rights Agreement has been filed with the Securities and Exchange Commission by
priceline.com and is incorporated herein by reference.

<PAGE>   6
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 6 of 13 Pages
------------------------                                -----------------------

                  A copy of the agreement pursuant to which Delta became a party
to the Registration Rights Agreement is filed as an exhibit to this statement
and is incorporated herein by reference.

                  In connection with the proposed public offering of
priceline.com common stock, certain stockholders of priceline.com have assigned
Delta their rights to sell shares in the proposed offering. A copy of the
assignment is filed as an exhibit to this statement and is incorporated herein
by reference.


ITEM 5            INTEREST IN SECURITIES OF PRICELINE.COM

                  (a) Delta is the beneficial owner of 9,309,701 shares of
priceline.com's common stock, all of which are issuable to Delta upon the
exercise of its warrant. The shares beneficially owned by Delta represent
approximately 6.1% of priceline.com's outstanding common stock (calculated as
required by Rule 13d-3(d)(1) and assuming that there are 142,320,427 shares of
priceline.com common stock outstanding, as reported in priceline.com's Quarterly
Report on Form 10-Q for the period ended March 31, 1999).

                  Mary Johnston Evans, a director of Delta, holds 100 shares of
priceline.com common stock. To the best of Delta's knowledge, none of the other
directors or executive officers of Delta beneficially owns shares of
priceline.com's common stock.

                  (b) Delta has sole voting and dispositive power over all of
the shares of priceline.com's common stock Delta beneficially owns and, to the
best of Delta's knowledge, Mary Johnston Evans has sole voting and dispositive
power over all of the shares of priceline.com's common stock she holds.

                  (c) Except as otherwise set forth in this statement, neither
Delta nor, to the best of Delta's knowledge, any of Delta's directors or
executive officers has effected any transactions in priceline.com's common stock
during the past 60 days.

                  (d) No person other than Delta has the right to receive or the
power to direct the receipt of dividends from, or the proceeds from the sale of,
the shares of priceline.com's common stock beneficially owned by Delta or, to
the best of Delta's knowledge, Mary Johnston Evans.

                  (e) Delta has not ceased being the beneficial owner of more
than 5% of priceline.com's outstanding common stock.

ITEM 6            CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH
                  RESPECT TO SECURITIES OF PRICELINE.COM

                  As described in Item 3 above, Delta holds a warrant to
purchase 18,619,402 shares of priceline.com's common stock. The warrant, which
has an exercise price of $0.9254896 per share, is currently exercisable with
respect to 9,309,701 shares and will become exercisable with respect to the
balance of the shares on December 31, 2005, or earlier if certain performance
thresholds are achieved. The warrant expires on December 31, 2005 (or June 30,
2006, if the warrant does not become exercisable until December 31, 2005).

<PAGE>   7
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 7 of 13 Pages
------------------------                                -----------------------

                  As described in Item 4 above, Delta is a party to and an
assignee of certain rights under a Registration Rights Agreement with respect to
priceline.com's common stock. A copy of the Registration Rights Agreement has
been filed with the Securities and Exchange Commission by priceline.com and is
incorporated herein by reference. Copies of the agreements pursuant to which
Delta became a party to and an assignee of certain rights under the Registration
Rights Agreement are filed as exhibits to this statement and are incorporated
herein by reference.

                  In connection with priceline.com's initial public offering of
common stock, Delta agreed not to engage in sales, transfers or similar
transactions involving priceline.com's common stock without the prior written
consent of Morgan Stanley & Co. Incorporated prior to 180 days after March 29,
1999. A copy of this agreement is filed as an exhibit to this statement and is
incorporated by reference into this statement.

ITEM 7            MATERIAL TO BE FILED AS EXHIBITS

Exhibit                          Description
-------                          -----------

1        Participation Warrant Agreement, dated August 31, 1998, between
         priceline.com and Delta. (1)

2        First Amendment and Waiver to Participation Warrant Agreement, dated
         December 31, 1998, between priceline.com and Delta.(1)*

3        Amended and Restated Registration Rights Agreement, dated as of
         December 8, 1998, among priceline.com and certain stockholders and
         warrantholders of priceline.com. (2)

4        Acknowledgment and Agreement to the Amended and Restated Registration
         Rights Agreement, dated July 16, 1999, between Delta and priceline.com.

5        Assignment of Certain Registration Rights, dated as of July 16, 1999,
         by and among Delta and the assignors named therein.

6        Airline Participation Agreement, dated August 31, 1998, by and among
         Delta, priceline.com and Priceline Travel, Inc. (1) *

7        General Agreement, dated August 31, 1998, by and among Delta,
         priceline.com and Priceline Travel, Inc. (1) *

8        Amendment to the Airline Participation Agreement and the General
         Agreement, dated December 31, 1998, between and among priceline.com,
         Priceline Travel, Inc. and Delta. (1)*

9        Lock-up Agreement, dated February 22, 1999.

<PAGE>   8
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 8 of 13 Pages
------------------------                                -----------------------

-------------------------------

(1)  Incorporated by reference to priceline.com's Registration Statement on Form
     S-1, No. 333-69657, as filed on February 16, 1999.

(2)  Incorporated by reference to priceline.com's Registration Statement on Form
     S-1, No. 333-69657, as filed on December 23, 1998.

* Portions of this exhibit have been omitted pursuant to a confidential
treatment request.





<PAGE>   9

------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 9 of 13 Pages
------------------------                                -----------------------


                                    SIGNATURE

                  After reasonable inquiry and to the best of my knowledge and
belief, I certify that the information set forth in this statement is true,
complete and correct.



Dated:  July 21, 1999           Delta Air Lines, Inc.


                                By: /s/ Warren C. Jenson
                                   --------------------------------------------
                                   Warren C. Jenson
                                   Executive Vice President and Chief Financial
                                   Officer


<PAGE>   10

------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 10 of 13 Pages
------------------------                                -----------------------


                                   SCHEDULE A


<TABLE>
<CAPTION>


                                                                                PRESENT PRINCIPAL OCCUPATION (IF OTHER
NAME AND ADDRESS                                    POSITION WITH DELTA         THAN POSITION WITH DELTA)
<S>                                                 <C>                         <C>
Gerald Grinstein                                    Chairman                    Non-Executive Chairman of the Board, Delta
1000 2nd Avenue, Suite 3700                                                     Air Lines, Inc.; Retired Chairman,
Seattle, Washington 98104                                                       Burlington Northern Santa Fe Corporation;
                                                                                Retired Chairman and Chief Executive
                                                                                Officer, Burlington Northern Inc., Fort
                                                                                Worth, Texas; former Chief Executive
                                                                                Officer, Western Air Lines, Inc.

Leo F. Mullin                                       President, Chief
Delta Air Lines, Inc.                               Executive Officer and
Hartsfield Atlanta International Airport            Director
Atlanta, Georgia  30320

Edwin L. Artzt                                      Director                    Chairman of the Board, Spalding Sports
Delta Air Lines, Inc.                                                           Worldwide, Inc.; Retired Chairman of the
Hartsfield Atlanta International Airport                                        Board and Chief Executive Officer, The
Atlanta, Georgia  30320                                                         Procter & Gamble Company, Cincinnati, Ohio


Henry A. Biedenharn, III                            Director                    Retired Chairman of the Board, President
Delta Air Lines, Inc.                                                           and Chief Executive Officer, Ouachita
Hartsfield Atlanta International Airport                                        Coca-Cola Bottling Company, Inc., Monroe,
Atlanta, Georgia  30320                                                         Louisiana


James L. Broadhead                                  Director                    Chairman of the Board and Chief Executive
P.O. Box 14000                                                                  Officer, FPL Group, Inc.; Chairman of the
Juno Beach, Florida  33408                                                      Board and Chief Executive Officer, Florida
                                                                                Power & Light Company, Juno Beach, Florida

Edward H. Budd                                      Director                    Retired Chairman of the Board and Chief
Delta Air Lines, Inc.                                                           Executive Officer, The Travelers
Hartsfield Atlanta International Airport                                        Corporation, Hartford, Connecticut
Atlanta, Georgia  30320

R. Eugene Cartledge
6 Skidaway Village Walk Suite 203-B                 Director                    Former Chairman of the Board, Savannah
Savannah, Georgia 31411-2913                                                    Foods & Industries, Inc., Savannah,
                                                                                Georgia; Retired Chairman of the Board and
                                                                                Chief Executive Officer, Union Camp
                                                                                Corporation, Wayne, New Jersey
</TABLE>



<PAGE>   11
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 11 of 13 Pages
------------------------                                -----------------------




<TABLE>
<CAPTION>

                                                                                PRESENT PRINCIPAL OCCUPATION (IF OTHER
NAME AND ADDRESS                                    POSITION WITH DELTA         THAN POSITION WITH DELTA)
<S>                                                 <C>                         <C>
Mary Johnston Evans                                 Director                    Director of various corporations
Delta Air Lines, Inc.
Hartsfield Atlanta International Airport
Atlanta, Georgia  30320


David R. Goode                                      Director                    Chairman, President and Chief Executive
Norfolk Southern Corporation                                                    Officer of Norfolk Southern Corporation
Three Commercial Place
Norfolk, Virginia  23510-2191

Andrew J. Young                                     Director                    Chairman and Senior Partner, Goodworks
303 Peachtree Street, N.E.                                                      International, Inc., Atlanta, Georgia;
Atlanta, Georgia  30311                                                         Chairman of the Southern Africa Enterprise
                                                                                Development Fund; former Mayor of Atlanta,
                                                                                Georgia; former U.S. Ambassador to the
                                                                                United Nations; former member of the U.S.
                                                                                House of Representatives


Maurice W. Worth                                    Chief Operating Officer
Delta Air Lines, Inc.
Hartsfield Atlanta International Airport
Atlanta, Georgia  30320

Malcolm B. Armstrong                                Executive Vice President
Delta Air Lines, Inc.                               - Operations
Hartsfield Atlanta International Airport
Atlanta, Georgia  30320

Robert L. Colman                                    Executive Vice President
Delta Air Lines, Inc.                               - Human Resources
Hartsfield Atlanta International Airport
Atlanta, Georgia  30320

Vicki B. Escarra                                    Executive Vice President
Delta Air Lines, Inc.                               - Customer Service
Hartsfield Atlanta International Airport
Atlanta, Georgia  30320

Warren C. Jenson                                    Executive Vice President
Delta Air Lines, Inc.                               and Chief Financial
Hartsfield Atlanta International Airport            Officer
Atlanta, Georgia  30320
</TABLE>



<PAGE>   12
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 12 of 13 Pages
------------------------                                -----------------------




<TABLE>
                                                                                PRESENT PRINCIPAL OCCUPATION (IF OTHER
NAME AND ADDRESS                                    POSITION WITH DELTA         THAN POSITION WITH DELTA)
<S>                                                 <C>                         <C>
Frederick W. Reid                                   Executive Vice President
Delta Air Lines, Inc.                               and Chief Marketing
Hartsfield Atlanta International Airport            Officer
Atlanta, Georgia  30320
</TABLE>




<PAGE>   13
------------------------                                -----------------------
CUSIP NO.   741503106                                   Page 13 of 13 Pages
------------------------                                -----------------------

                                 EXHIBIT INDEX
                                 -------------

Exhibit                          Description
-------                          -----------

1        Participation Warrant Agreement, dated August 31, 1998, between
         priceline.com and Delta. (1)

2        First Amendment and Waiver to Participation Warrant Agreement, dated
         December 31, 1998, between priceline.com and Delta.(1)*

3        Amended and Restated Registration Rights Agreement, dated as of
         December 8, 1998, among priceline.com and certain stockholders and
         warrantholders of priceline.com. (2)

4        Acknowledgment and Agreement to the Amended and Restated Registration
         Rights Agreement, dated July 16, 1999, between Delta and priceline.com.

5        Assignment of Certain Registration Rights, dated as of July 16, 1999,
         by and among Delta and the assignors named therein.

6        Airline Participation Agreement, dated August 31, 1998, by and among
         Delta, priceline.com and Priceline Travel, Inc. (1) *

7        General Agreement, dated August 31, 1998, by and among Delta,
         priceline.com and Priceline Travel, Inc. (1) *

8        Amendment to the Airline Participation Agreement and the General
         Agreement, dated December 31, 1998, between and among priceline.com,
         Priceline Travel, Inc. and Delta. (1)*

9        Lock-up Agreement, dated February 22, 1999.

-------------------------------

(1)  Incorporated by reference to priceline.com's Registration Statement on Form
     S-1, No. 333-69657, as filed on February 16, 1999.

(2)  Incorporated by reference to priceline.com's Registration Statement on Form
     S-1, No. 333-69657, as filed on December 23, 1998.

* Portions of this exhibit have been omitted pursuant to a confidential
treatment request.








<PAGE>   1


                                                                       Exhibit 4


                          ACKNOWLEDGMENT AND AGREEMENT
            TO THE AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT

         WHEREAS, pursuant to a Participation Warrant Agreement, Delta Air
Lines, Inc. ("Delta") received a warrant to purchase 18,619,402 shares of common
stock (as adjusted for the 1.25 for 1 stock split effected March 26,1999), par
value $.008 per share (the "Shares"), of priceline.com Incorporated, a Delaware
corporation (the "Company"); and

         WHEREAS, Delta wishes to receive certain registration rights with
respect to such Shares; and

         WHEREAS, Delta has reviewed a copy of that certain Amended and Restated
Registration Rights Agreement, dated as of December 8, 1998 (the "Agreement"),
among the Company, General Atlantic Partners 48, L.P., GAP Coinvestment
Partners, L.P., General Atlantic Partners 50, L.P. and the stockholders named
therein and has been given a copy of the Agreement and afforded ample
opportunity to read and to have counsel review it, and Delta is thoroughly
familiar with its terms.

         NOW, THEREFORE, in consideration of the mutual premises contained
herein and in the Agreement and for other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, Delta hereby
acknowledges and agrees
 as follows: (i) Delta has been given a copy of the
Agreement and afforded ample opportunity to read and to have counsel review it,
and Delta is thoroughly familiar with its terms, (ii) the Shares are subject to
terms and conditions set forth in the Agreement, (iii) Delta does hereby agree
fully to be bound by the Agreement as a "Demand Stockholder" (as therein
defined), and upon the execution and delivery of this Acknowledgment and
Agreement by the Company, Delta shall have all the rights and obligations under
the Agreement as a Demand Stockholder, and (iv) Delta does hereby name Edward H.
West to serve as its representative under the Agreement.

         The Company hereby represents and warrants to Delta that the Board of
Directors of the Company has duly approved Delta as "Demand Stockholder" as is
required by the Agreement.

         This 16th day of July, 1999.

Acknowledged and agreed:
PRICELINE.COM INCORPORATED            DELTA AIR LINES, INC.

By   /s/ Paul Francis                 By:   /s/ Edward H. West
  ------------------------------         --------------------------------------
   Name:  Paul Francis                   Name: Edward H. West
   Title:                                Title: Sr. Vice President -- Strategy
                                                and Business Development






<PAGE>   1



                                                                       Exhibit 5

                    ASSIGNMENT OF CERTAIN REGISTRATION RIGHTS

         This Assignment of Certain Registration Rights (the "Assignment") dated
as of July 16, 1999, by and among Jay S. Walker, Richard S. Braddock and The Jay
S. Walker Irrevocable Credit Trust (collectively "Assignors") and Delta Air
Lines, Inc. ("Delta").

         WHEREAS, Assignors are each Major Stockholders and Delta is a Demand
Stockholder under that certain Amended and Restated Registration Rights
Agreement dated as of December 8, 1998 (the "Rights Agreement"), by and among
priceline.com Incorporated (the "Company"), General Atlantic Partners 48, L.P.,
GAP Coinvestment Partners, L.P., General Atlantic Partners 50, L.P. and the
other stockholders and warrant holders named therein or made a party thereto.
Capitalized terms used herein and not otherwise defined shall have the meanings
ascribed to them in the Rights Agreement;

         WHEREAS, the Company has provided notice to the parties to the Rights
Agreement of its intention to file a registration statement under the Securities
Act of 1933, as amended, on Form S-1 for the offering by the Company of Two
Million (2,000,000) shares of its Common Stock and an "Incidental Registration"
(as such term is defined in Section 4(a) of the Rights Agreement)
 for the
offering of up to Four Million Nine Hundred Thousand (4,900,000) shares
(inclusive of over-allotment shares) of common stock by certain selling
stockholders including one or more of the Assignors and Delta (collectively, the
"Proposed Offering"); and

         WHEREAS, in connection with the Proposed Offering, the Assignors desire
to assign, and Delta desires to receive the assignment of, certain registration
rights of Assignors under the Rights Agreement.

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained and other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:

         1.       Assignment of Incidental Registration Rights.


                  (a)      The Assignors, collectively, in respect to their
                           rights under Section 4(a) of the Rights Agreement to
                           offer Registrable Securities specifically in the
                           Incidental Registration comprising a part of the
                           Proposed Offering ("Assignors' Registration Rights"),
                           hereby assign to Delta that portion of Assignors'
                           Registration Rights to offer for sale that number of
                           shares that, when aggregated with the rights of
                           Delta, as a Designated Holder, will entitle Delta to
                           offer for sale an aggregate of 36.2% of all shares
                           (inclusive of over-allotment shares) of the

<PAGE>   2

                           Company's Common Stock to be offered by all selling
                           stockholders in the Proposed Offering.

                  (b)      In connection with the Proposed Offering, Jay S.
                           Walker hereby covenants and agrees to not sell any
                           shares in the Proposed Offering.

                  (c)      With respect to any of their shares not sold in the
                           Proposed Offering, Assignors hereby agree to sign the
                           lockup agreement that will be required by the
                           Company's underwriters to be signed by all selling
                           stockholders in the Proposed Offering.

                  2.       Consent of the Company. The parties hereto
acknowledge that this Assignment is being effected in accordance with the
provisions of Section 10(f) of the Rights Agreement, and therefore requires the
consent of the Company. The Company's consent to this Assignment, as evidence on
the signature page hereof, is provided solely to satisfy the provisions of
Section 10(f) of the Rights Agreement.

                           [Signature Page to Follow]



<PAGE>   3


         IN WITNESS WHEREOF, the parties have executed this Assignment as of the
date and year first above written.

ASSIGNORS:                            DELTA AIR LINES, INC.



      /s/ Jay S. Walker               By:        /s/ Edward H. West
--------------------------------         --------------------------------------
Jay S. Walker                            Name: Edward H. West
                                         Title:  Sr. Vice President -- Strategy
                                                 and Business Development


      /s/ Richard S. Braddock
--------------------------------
Richard S. Braddock



THE JAY S. WALKER
IRREVOCABLE CREDIT TRUST


By:   /s/ Harry E. Peden, III
--------------------------------
Harry E. Peden, III
Trustee


CONSENTED TO BY:


PRICELINE.COM INCORPORATED


By:   /s/ Paul Francis
--------------------------------
Name:
Title:





<PAGE>   1




                                                                      Exhibit 9

                                        February 22, 1999



Morgan Stanley & Co. Incorporated
Merrill Lynch, Pierce, Fenner & Smith
Incorporated

BancBoston Robertson Stephens Inc.
Donaldson, Lufkin & Jenrette Securities
Corporation

c/o Morgan Stanley & Co. Incorporated
1585 Broadway
New York, New York  10036

Morgan Stanley & Co. International Limited
Merrill Lynch International
BancBoston Robertson Stephens Inc.
Donaldson, Lufkin & Jenrette International
c/o Morgan Stanley & Co. International Limited
25 Cabot Square
Canary Wharf
London E14 4QA
England

Dear Sirs and Mesdames:

         The undersigned understands that Morgan Stanley & Co. Incorporated
("Morgan Stanley") and Morgan Stanley & Co. International Limited ("MSIL")
propose to enter into an Underwriting Agreement with priceline.com Incorporated
("priceline.com") providing for the public offering (the "Public Offering") by
the several underwriters, including Morgan Stanley and MSIL (the
"Underwriters"), of shares of the Common Stock, par value $.01 per share, of
priceline.com (the "Common Stock").

         To induce the Underwriters that may participate in the Public Offering
to continue their efforts in connection with the Public Offering, the
undersigned hereby agrees, that, without the prior written consent
 of Morgan
Stanley on behalf of the Underwriters, the undersigned will not, during the
period commencing on the date hereof and ending 180 days after the date of the
final prospectus relating to the Public Offering (the "Prospectus"), (1) offer,
pledge, sell, contract to sell, sell any option or contract to purchase,
purchase any option or contract to sell, grant any option, right or warrant to
purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any
shares of Common Stock or any securities convertible into or exercisable or
exchangeable for Common Stock or (2) enter into any swap or other arrangement
that transfers to another, in whole or in part, any of the


<PAGE>   2

economic consequences of ownership of the Common Stock, whether any such
transaction described in clause (1) or (2) above is to be settled by delivery of
Common Stock or such other securities, in cash or otherwise. In addition, the
undersigned agrees that, without the prior written consent of Morgan Stanley on
behalf of the Underwriters, the undersigned will not, during the period
commencing on the date hereof and ending 180 days after the date of the
Prospectus, make any demand for or exercise any right with respect to, the
registration of any shares of Common Stock or any security convertible into or
exercisable or exchangeable for Common Stock.

         Whether or not the Public Offering actually occurs depends on a number
of factors, including market conditions. Any Public Offering will only be made
pursuant to an Underwriting Agreement, the terms of which are subject to
negotiation between priceline.com and the Underwriters. In the event that the
Public Offering shall not have been consummated on or before May 15, 1999, this
Lock-Up Agreement shall be of no further force or effect.

                                     Very truly yours,

                                     DELTA AIR LINES, INC.



                                     By:      /s/ Warren Jenson
                                        -------------------------------------
                                         Name:  Warren C. Jenson
                                         Title:  Executive Vice President & CFO
                                         Address:  P.O. Box 20706
                                         Atlanta, Georgia  30320-6001