<PAGE>
                                                                 Exhibit 10.3(b)


                      FOURTH AMENDMENT TO CREDIT AGREEMENT


                  THIS FOURTH AMENDMENT TO CREDIT AGREEMENT (the "Amendment")
dated and effective as of October 10, 2002, is made by and among FREEMARKETS,
INC., a Delaware corporation (the "Borrower"), the Banks (as hereinafter
defined), SILICON VALLEY BANK, individually and in its capacity as Syndication
Agent (the "Syndication Agent"), and PNC BANK, NATIONAL ASSOCIATION, in its
capacity as administrative agent for the Banks (hereinafter referred to in such
capacity as the "Agent").

                              W I T N E S S E T H:

                  WHEREAS, reference is made to that certain Credit Agreement,
dated as of November 3, 2000, by and among Borrower, the Banks from time to time
party thereto (the "Banks"), the Syndication Agent, and the Agent, as amended by
a First Amendment thereto dated as of December 8, 2000, a Second Amendment
thereto dated as of February 7, 2001, and a Third Amendment thereto dated as of
October 31, 2001 (as so amended, the "Credit Agreement"); and

                  WHEREAS, the parties hereto desire to amend certain terms
thereof as hereinafter provided.

                  NOW, THEREFORE, the parties hereto, in consideration of their
mutual covenants and agreements hereinafter set forth and intending to be
legally bound hereby, covenant and agree as follows:

1. Definitions.

                  Capitalized terms used herein unless otherwise defined herein
shall have the meanings ascribed to them in the Credit Agreement as amended by
this Amendment.

2. Amendment of Credit Agreement.

                  The definition of "Expiration Date" as set forth in Section
1.1 of the Credit Agreement is hereby amended and restated in its entirety to
read as follows:

                  "Expiration Date shall mean, with respect to the Revolving
Credit Commitments, December 30, 2002, as such date may be hereafter extended in
accordance with Section 2.10 hereof.

3. Representations and Warranties. The Borrower hereby represents and warrants
to the Banks, the Syndication Agent, and the Agent that, as of the date of and
after giving effect to this Amendment, (a) the execution, delivery and
performance of this Amendment and any and all other documents executed and/or
delivered in connection herewith have been authorized by all requisite corporate
action on the part of the Borrower and will not violate the Borrower's articles
of incorporation or bylaws, (b) no Event of Default or Potential Event of
Default has occurred and is continuing or would result from the making of this
Amendment, (c) the representations and warranties of the Loan Parties contained
in the Credit Agreement are true and correct on and as of the date hereof with
the same force and effect as though made by the Loan Parties on such

<PAGE>


date (except representations and warranties which relate solely to an earlier
date or time), and (d) the Credit Agreement (as amended by a First Amendment
thereto dated as of December 8, 2000, a Second Amendment thereto dated as of
February 7, 2001, a Third Amendment thereto dated as of October 31, 2001, and
this Amendment) and all other Loan Documents are and remain legal, valid,
binding and enforceable obligations in accordance with the terms thereof.

4. Conditions of Effectiveness of this Amendment. The effectiveness of this
Amendment is expressly conditioned upon satisfaction of each of the following
conditions precedent:

         A. Fees and Expenses. The Borrower shall pay or cause to be paid to the
Agent for itself and for the account of the Banks the reasonable costs and
expenses of the Agent and the Banks including, without limitation, reasonable
fees of the Agent's counsel in connection with this Amendment.

         B. No Default. As of the date hereof, no Event of Default or Potential
Default has occurred and is continuing and Borrower by executing this Amendment
confirms the same and also confirms the accuracy of the representations and
warranties in Section 3 above.

         C. Confirmation of Guaranty. Each of the Guarantors shall have executed
the Confirmation of Guaranty in the form attached hereto as Exhibit A.

         D. Execution by the Banks and the Loan Parties. The Agent shall have
received from the Borrower, each Guarantor, and the Banks an executed original
of this Amendment.

This Amendment shall become effective when it has been executed by the Loan
Parties and the Banks and each of the other conditions set forth in this Section
4 has been satisfied.

5. Amendment. The Credit Agreement and other Loan Documents referred to herein
and certain of the exhibits and schedules thereto are hereby amended in
accordance with the terms hereof and any reference to the Credit Agreement or
other Loan Documents in any document, instrument, or agreement shall hereafter
mean and include the Credit Agreement or such Loan Document, including such
schedules and exhibits, as amended hereby. No novation is intended or shall
occur by or as a result of this Amendment.

6. Force and Effect. Borrower reconfirms, restates, and ratifies the Credit
Agreement and all other documents executed in connection therewith except to the
extent any such documents are expressly modified by this Amendment and each of
the Loan Parties confirms that all such documents have remained in full force
and effect since the date of their execution.

7. Governing Law. This Amendment shall be deemed to be a contract under the laws
of the Commonwealth of Pennsylvania and for all purposes shall be governed by
and construed and enforced in accordance with the internal laws of the
Commonwealth of Pennsylvania without regard to its conflict of laws principles.


<PAGE>

8. Counterparts. This Amendment may be signed in any number of counterparts each
of which shall be deemed an original, but all of which together shall constitute
one and the same instrument.


                         [SIGNATURES BEGIN ON NEXT PAGE]


<PAGE>




         [SIGNATURE PAGE 1 OF 3 TO FOURTH AMENDMENT TO CREDIT AGREEMENT]


         IN WITNESS WHEREOF and intending to be legally bound hereby, the
parties hereto have executed this Amendment as of the date first above written.


ATTEST:                                 FREEMARKETS, INC.


                                        By:  /s/ Joan Hooper            [Seal]
-------------------------------             -----------------------------
Name:                                   Name:    Joan Hooper
      -------------------------               ---------------------------
Title:                                  Title:   Executive VP & CFO
       ------------------------               ---------------------------







<PAGE>



         [SIGNATURE PAGE 2 OF 3 TO FOURTH AMENDMENT TO CREDIT AGREEMENT]


                                        PNC BANK, NATIONAL ASSOCIATION,
                                        individually and as Agent



                                        By:   /s/ Thomas A. Majewski
                                            -----------------------------------
                                        Name:     Thomas A. Majewski
                                              ---------------------------------
                                        Title:    Vice President
                                              ---------------------------------




<PAGE>



         [SIGNATURE PAGE 3 OF 3 TO FOURTH AMENDMENT TO CREDIT AGREEMENT]


                                        SILICON VALLEY BANK, individually
                                        and as Syndication Agent



                                        By:   /s/ R. B. Hamilton
                                            ----------------------------------
                                        Name:     Robert B. Hamilton
                                              --------------------------------
                                        Title:    Vice President
                                              --------------------------------




<PAGE>



                                    EXHIBIT A

                            CONFIRMATION OF GUARANTY


                                October 10, 2002


To:      FreeMarkets Investment Company, Inc. ("Guarantor")

         Reference is made to that certain Credit Agreement, dated as of
November 3, 2000, as amended by a First Amendment thereto dated as of December
8, 2000, a Second Amendment thereto dated as of February 7, 2001, a Third
Amendment thereto dated as of October 31, 2001, and the Fourth Amendment (as
defined below) (the "Credit Agreement"), by and among FreeMarkets, Inc., a
Delaware corporation (the "Borrower"), the Banks from time to time party thereto
(the "Banks"), Silicon Valley Bank, individually and in its capacity as
Syndication Agent and PNC Bank, National Association, as administrative agent
for the Banks ("Agent"). All terms used herein unless otherwise defined herein
shall have the meanings as set forth in the Credit Agreement.

         The Borrower has requested that the Banks and the Agent enter into that
certain Fourth Amendment to the Credit Agreement, dated as of the date hereof
(the "Fourth Amendment"), a copy of which has been delivered to each Loan Party.

         This letter agreement will confirm that the Guarantor has read and
understands the Fourth Amendment. In order to induce the Banks and the Agent to
enter into that Fourth Amendment, the Guarantor hereby consents to the Fourth
Amendment and all prior amendments described above and ratifies and confirms its
respective obligations under each of the Loan Documents (including all exhibits
and schedules thereto) to which it is a party by signing below as indicated,
including without limitation each Guaranty Agreement and each Security Agreement
to which it is a party. The Guarantor hereby acknowledges and agrees that
nothing contained in any of the Loan Documents is intended to create, nor shall
it constitute an interruption, suspension of continuity, satisfaction, discharge
of prior duties, novation or termination of the liens, security interests,
indebtedness, loans, liabilities, expenses or obligations of the Loan Parties
under the Credit Agreement or any other Loan Document.

                                        Very truly yours,

                                        PNC BANK, NATIONAL ASSOCIATION, as Agent


                                        By: /s/ Thomas A. Majewski
                                            -----------------------------------


<PAGE>


                   [SIGNATURE PAGE TO CONFIRMATION OF GUARANTY
                            DATED OCTOBER 10, 2002]




Intending to be legally bound
hereby, the undersigned has
accepted and agreed to the
foregoing as of the date and
year first above written.


GUARANTOR:

FREEMARKETS INVESTMENT COMPANY, INC.



By: /s/ Gerard J. Bernard
    --------------------------------
Name:  Gerard J. Bernard
      ------------------------------
Title: President
      ------------------------------