<PAGE>

                                                                    Exhibit 4.21

                               SECOND AMENDMENT TO
                           FOURTH AMENDED AND RESTATED
                    REVOLVING CREDIT AND TERM LOAN AGREEMENT

      This SECOND AMENDMENT, dated as of March 31, 1997, by and among (a)
Griffith Consumers Company ("Griffith"), Shore Stop Corporation ("SSC"), and
Carl King, Inc. ("King"), each a Delaware corporation, (collectively, the
"Borrowers"), (b) BankBoston, N.A. (f/k/a The First National Bank of Boston).
The Travelers Insurance Company, The Travelers Indemnity Company, Senior Debt
Portfolio and Riggs Bank N.A. (collectively, the "Banks") and (c) BankBoston,
N.A. as agent for the Banks (the "Agent").

      WHEREAS, the Borrowers, the Banks and the Agent are parties to that
certain Fourth Amended and Restated Revolving Credit and Term Loan Agreement
dated as of July 8, 1996 (as amended to date, the "Credit Agreement"), and

      WHEREAS, the Borrowers have requested and the Banks have agreed, subject
to the terms and conditions set forth herein, to modify certain provisions of
the Credit Agreement.

      NOW, THEREFORE, the Borrowers, the Banks and the Agent hereby covenant and
agree as follows:

      ss.1. Defined Terms. Capitalized terms which are used herein without
definition and which are defined in the Credit Agreement shall have the same
meanings herein as in the Credit Agreement.

      ss.2. Amendment to the Credit Agreement.

      (a) Section 1.1 of the Credit Agreement is hereby amended by inserting the
following definitions in the appropriate alphabetical order:

            Rebranding Expenditures. Expenditures incurred by the Borrower in
            connection with rebranding certain retail gasoline stations pursuant
            to the terms of the Reimbursement Agreements, including, without
            limitation, the cost of replacing signs and other station or brand
            identification.

            Rebranding Proceeds. Proceeds received by the Borrowers in
            connection with rebranding certain retail gasoline stations pursuant
            to the terms of the Reimbursement Agreements.

            Reimbursement Agreements. Collectively, the Reimbursement Agreement
            for Mobil Distributor dated April 17, 1997 between Mobil Oil
            Corporation and Carl King, Inc. and the Advance Agreement dated May
            20, 1997 between SSC and CITGO Petroleum Corporation (collectively,
            the "Reimbursement Agreements").

      (b) Section 11.1 of the Credit Agreement is hereby amended and restated in
its entirety to read as follows:
<PAGE>

                                       -2-


      11.1. Debt Service Coverage Ratio. For each period of four consecutive
fiscal quarters ending on a date set forth in the table below, the Borrowers
will not permit the Debt Service Coverage Ratio for such period to be less than
the amount set forth opposite the relevant period in the table below:

--------------------------------------------------------------------------------
           Period of Four Consecutive
           Fiscal Quarters ending:                             Ratio
           -----------------------                             -----
--------------------------------------------------------------------------------
           6/30/96 and 9/30/96                                 1.10:1.00
--------------------------------------------------------------------------------
           12/31/96                                            1.10:1.00
--------------------------------------------------------------------------------
           3/31/97                                             0.35:1.00
--------------------------------------------------------------------------------
           6/30/97 and 9/30/97                                 0.90:1.00
--------------------------------------------------------------------------------
           12/31/97                                            0.98:1.00
--------------------------------------------------------------------------------
           3/31/98 and thereafter                              1.10:1.00
--------------------------------------------------------------------------------

      (c) Section 11.2 of the Credit Agreement is hereby amended and restated in
its entirety to read as follows:

            11.2. Cash Flow Ratio. For each period of four consecutive fiscal
      quarters ending on a date set forth in the table below, commencing with
      the period of four consecutive fiscal quarters ending June 30, 1996, the
      Borrowers will not permit the ratio of (a) Consolidated Net Earnings
      Available for Debt Service calculated for the period of four consecutive
      fiscal quarters then ended after excluding therefrom to the extent
      otherwise included Rebranding Proceeds and Rebranding Expenditures plus
      (i) the aggregate proceeds from all Indebtedness which is permitted under
      ss.10.1(g) and (h) which is incurred by the Borrowers during such period
      to the extent that in accordance with generally accepted accounting
      principles the acquisition or Capitalized Lease in connection with which
      such Indebtedness arises was treated as a Capital Expenditure plus, (ii)
      subject to the limitation set forth below in this ss.11.2. for each period
      of four consecutive fiscal quarters which include one or more fiscal
      quarters which end in Fiscal Year 1997, Fiscal Year 1998 or Fiscal Year
      1999, the amount of Capital Expenditures (after excluding therefrom, to
      the extent otherwise included, Rebranding Expenditures) actually made in
      such period of four consecutive fiscal quarters in excess of $3,500,000,
      (provided that the Borrowers may, at their option, elect not to add back
      such excess amount for any period of four consecutive fiscal quarters if
      such fiscal quarters do not occur in a single Fiscal Year) plus (iii)
      Rebranding Proceeds after deducting therefrom Rebranding Expenditures to
      (b) Consolidated Debt Service calculated for such period plus
      Discretionary Capital Expenditures (after excluding therefrom, to the
      extent otherwise included, Rebranding Expenditures) made by the Borrowers
      and their Subsidiaries during such period, to be less than the amount set
      forth opposite the relevant period in the table below:

--------------------------------------------------------------------------------
           Period of Four Consecutive
           Fiscal Quarters ending:                                Ratio
           -----------------------                                -----
--------------------------------------------------------------------------------
           6/30/96 and 9/30/96                                    1.000:1.00
--------------------------------------------------------------------------------
           12/31/96                                               0.850:1.00
--------------------------------------------------------------------------------
           3/31/97                                                0.770:1.00
--------------------------------------------------------------------------------
           6/30/97                                                0.810:1.00
--------------------------------------------------------------------------------
<PAGE>

                                       -3-


--------------------------------------------------------------------------------
           9/30/97                                                0.830:1.00
--------------------------------------------------------------------------------
           12/31/97                                               0.900:1.00
--------------------------------------------------------------------------------
           3/31/98 through 3/31/00 (inclusive)                    1.000:1.00
--------------------------------------------------------------------------------
           6/30/00 and thereafter                                 1.100:1.00
--------------------------------------------------------------------------------

      Notwithstanding the foregoing, for purposes of calculating compliance with
      this covenant, the Borrowers may not add back Capital Expenditures
      pursuant to clause (a) (ii) of this ss.11.2 in an aggregate amount in
      excess of $5,000,000. For purposes of calculating compliance with this
      limitation, the aggregate amount of Capital Expenditures added back
      pursuant to clause (a) (ii) above shall be equal to the aggregate of the
      add back amounts attributed (as provided below) to each fiscal quarter
      (without duplication for each of the four times such fiscal quarter
      appears in the rolling four quarter periods for which compliance hereunder
      is calculated). The add back of Capital Expenditures shall be attributable
      to the fiscal quarter which is the last fiscal quarter in the period of
      four consecutive fiscal quarters with respect to which such add back first
      occurs.

      (d) Section 11.5 of the Credit Agreement is hereby amended and restated in
its entirety to read as follows:

            11.5. Capital Expenditures. With respect to each fiscal period set
      forth below, the Borrowers will not, and will not permit any of their
      Subsidiaries to, make Capital Expenditures (exclusive of any Capital
      Expenditures made by delivery of Permitted Seller Notes issued in such
      fiscal period and permitted under ss.10.1 but including any cash principal
      repayment made with respect to such Permitted Seller Notes in the period
      during which such repayments are made) or Investments made pursuant to
      Section 10.3(e) in such fiscal period that exceed, in the aggregate, the
      amount set forth below for such fiscal period:

--------------------------------------------------------------------------------
                                                     Capital Expenditures and
          Fiscal Period                              ss.10.3(e) Investments
          -------------                              ----------------------
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
          Fiscal Year ending 1996                         $ 1,500,000
--------------------------------------------------------------------------------
          Fiscal Year ending 1997                         $ 6,400,000
--------------------------------------------------------------------------------
          Fiscal Quarter ending 6/30/97                   $ 2,200,000
--------------------------------------------------------------------------------
          Fiscal Quarter ending 9/30/97                   $   600,000
--------------------------------------------------------------------------------
          Fiscal Quarter ending 12/31/97                  $   600,000
--------------------------------------------------------------------------------
          Fiscal Quarter ending 3/31/98                   $ 1,500,000
--------------------------------------------------------------------------------
          Fiscal Year ending 1998                         $ 4,000,000
--------------------------------------------------------------------------------
          Fiscal Year ending 1999                         $ 4,500,000
--------------------------------------------------------------------------------
          Each Fiscal Year Thereafter                     $ 3,500,000
--------------------------------------------------------------------------------

      provided, however, that (a) for purposes of this ss.11.5, Capital
      Expenditures shall be calculated exclusive of (i) up to $900,000 of
      Rebranding Expenditures which would otherwise be included as Capital
      Expenditures and (ii) Capital Expenditures of the type described in
      clauses (A) and (B) of ss.4.5.2(b) made in lieu of a mandatory prepayment
      of the Term Loans with the net cash proceeds from the sale of assets
      permitted under ss.10.5.2.; (b) the amount of Capital Expenditures which
      are permitted to be incurred in the Fiscal Year ending June 30, 1998 and
      which are not incurred in such year may be carried over and used in the
      Fiscal Years ending
<PAGE>

                                       -4-


      June 30, 1999 and June 30, 2000 and shall be deemed to be the first
      amounts utilized in such Fiscal Years; and (c) if during any other fiscal
      period set forth above the amount of Capital Expenditures permitted for
      that fiscal period is not so utilized, such unutilized amount may be
      utilized, and shall be deemed to be the first amount utilized, in the
      immediately succeeding fiscal period set forth in the table above only.

      (e) Section 11.6 of the Credit Agreement is hereby amended and restated in
its entirety to read as follows:

            11.6. Funded Debt to Consolidated EBITDA Ratio. The Borrowers will
      not permit the ratio of (a) Funded Debt as of the end of each period of
      four consecutive fiscal quarters of the Borrowers ending on a date set
      forth in the table below, commencing with the four quarter period ending
      June 30, 1996, to (6) Consolidated EBITDA for such period, to be more than
      the amount set forth opposite the relevant period in the table below:

--------------------------------------------------------------------------------
           Period of Four Consecutive
           Fiscal Quarters ending:                  Ratio
           -----------------------                  -----
--------------------------------------------------------------------------------
           6/30/96, 9/30/96 and 12/31/96            5.00:1.00
--------------------------------------------------------------------------------
           3/31/97, 6/30/97 and 9/30/97             5.75:1.00
--------------------------------------------------------------------------------
           12/31/97                                 5.25:1.00
--------------------------------------------------------------------------------
           3/31/98                                  4.75:1.00
--------------------------------------------------------------------------------
           6/30/98, 9/30/98 and 12/31/98            4.35:1.00
--------------------------------------------------------------------------------
           3/31/99                                  4.00:1.00
--------------------------------------------------------------------------------
           6/30/99 and thereafter                   3.50:1.00
--------------------------------------------------------------------------------

      ; provided that, for purposes of calculating the ratio of Funded Debt to
      Consolidated EBITDA (a) for any period, any Permitted Acquisition which
      occurred during such period shall be deemed to have occurred immediately
      prior to the beginning of such period; and (6) for each period of four
      fiscal quarters ending at any time from the Closing Date through and
      including June 30, 1997, Funded Debt shall be decreased by $5,000,000; and
      (c) for each period of four fiscal quarters ending at any time from and
      including September 30, 1997 through and including June 30, 1998, Funded
      Debt shall be decreased by $2,500,000.

      (f) Section 11.7 of the Credit Agreement is hereby amended by substituting
the figure "$15,000,000" for the figure $17,000,000" therein.

      ss.3. Consent to Asset Transfer. Subject to the satisfaction of the
conditions set forth herein, the Banks hereby consent to (i) the merger of any
Borrower with and into another Borrower and to the transfer of any assets of a
Borrower from such Borrower to any other Borrower; provided that after giving
effect to each such merger and/or transfer, the Agent continues to have a first
priority perfected security interest (subject only to Permitted Liens) in such
transferred assets, or, if applicable, the assets of the merged Borrower
pursuant to the terms of the Loan Documents in order to secure the Obligations,
(ii) the transfer to a wholly-owned subsidiary of Griffith of assets currently
owned by King which do not consist of assets comprising or used in connection
with retail service stations or convenience stores; provided that such assets
remain subject to a first priority perfected security interest (subject only to
Permitted Liens) in favor of the Agent to secure the Obligations under the Loan
<PAGE>

                                       -5-


Agreement and such wholly-owned Subsidiary is or assumes the obligations of a
Borrower under the Credit Agreement or is or becomes a guarantor of the
Obligations pursuant to a guaranty in form and substance satisfactory to the
Agent and (iii) the transfer by Griffith of the outstanding shares of capital
stock of King to SSC or, alternatively, the transfer by Griffith of the
outstanding shares of capital stock of SSC to King. This consent is conditioned
upon the delivery by the Borrower to the Agent and the Banks of prior written
notice detailing the terms of such merger or transfer.

      ss.4. Conditions to Effectiveness. This Amendment shall become effective
upon satisfaction of each of the following conditions precedent:

      (a) receipt by the Agent of this Amendment, executed and delivered by each
of the Borrowers, the Agent and the Banks;

      (b) payment of an amendment fee to the Agent for the account of the Banks
in an aggregate amount equal to 0.125% of the aggregate principal amount of the
Term Loans outstanding plus the aggregate of each Bank's Revolving Credit
Commitment, such amendment fee to be shared pro rata by the Banks in accordance
with each Bank's percentage interest in the sum of (i) the aggregate principal
amount of the Term Loans outstanding and (ii) the Revolving Credit Commitments;
and

      (c) a copy, certified to be accurate and complete on the date hereof by a
duly authorized officer of the Company, of the executed Third Supplemental
Indenture of even date herewith (the "Supplemental Indenture") to the Indenture
dated as of December 15, 1994 among the Borrowers, Frederick and NationsBank
Trust Company of New York as trustee. such amendment to be in form and substance
satisfactory to the Agent in all respects; provided that in any event, (i) the
Supplemental Indenture shall include amendments to Section 4.21 of the Indenture
which reset the covenant levels therein to 90% of the covenant levels in Section
11.1 of the Credit Agreement, as amended hereby, and 110% of the covenant levels
in Section 11.6 of the Credit Agreement, as amended hereby, and (ii) any
amendment fee payable to the holders of Subordinated Debt evidenced by such
Subordinated Debt Documents in connection with the Supplemental Indenture shall
be disclosed to the Banks and the Agent in writing and shall be acceptable to
the Banks and the Agent.

      ss.5. Affirmation of the Borrowers. Each of the Borrowers hereby affirms
all of its obligations under the Credit Agreement, as amended hereby, the Notes
and under each of the other Loan Documents to which it is a party and hereby
affirms its absolute and unconditional promise to pay to the Banks the Loans and
all other amounts due under the Credit Agreement, as amended hereby. Each of the
Borrowers hereby represents, warrants and confirms that the Obligations, as
amended hereby, are and remain secured pursuant to the Security Documents.

      ss.6. Representations and Warranties. Each of the Borrowers hereby
represents and warrants to the Banks and the Agent as follows:

      (a) Representations and Warranties. The representations and warranties
contained in ss.8 of the Credit Agreement were true and correct in all material
respects when made. The representations and warranties contained in ss.8 of the
Credit Agreement, after giving effect to this Amendment, are true and correct on
the date hereof, except (i) for those representations and warranties which
relate specifically to a particular date, which representations and warranties
were true and correct as of such
<PAGE>

                                       -6-


date and (ii) as otherwise disclosed in writing by the Borrowers to each of the
Banks and the Agent subsequent to the Closing Date.

      (b) Authority. The execution and delivery by each Borrower of this
Amendment and the Additional Notes, and the performance by each Borrower of this
Amendment, the Additional Notes and the Credit Agreement, as amended hereby, (i)
are within the corporate authority of such Borrower, (ii) have been duly
authorized by all necessary corporate proceedings, (iii) do not conflict with or
result in any breach or contravention of any provision of law, statute, rule or
regulation to which such Borrower is subject or any judgment, order, writ,
injunction, license or permit applicable to such Borrower, and (iv) do not
conflict with any provision of the corporate charter or bylaws of such Borrower
or any agreement or other instrument binding upon such Borrower.

      (c) Enforceability. This Amendment, the Additional Notes and the Credit
Agreement, as amended hereby, are valid and legally binding obligations of each
Borrower, enforceable against such Borrower in accordance with their respective
terms and provisions, except as enforceability is limited by bankruptcy,
insolvency, reorganization, moratorium or other laws relating to or affecting
generally the enforcement of creditor's rights and except to the extent that
availability of the remedy of specific performance or injunctive relief is
subject to the discretion of the court before which any proceeding therefor may
be brought.

      (d) No Default. No Default or Event of Default exists or will exist after
giving effect to the execution and delivery of this Amendment.

      ss.7. No Other Amendments. Except as expressly provided in this Amendment,
all of the terms and conditions of the Credit Agreement and the other Loan
Documents remain unchanged, and the terms and conditions of the Credit Agreement
as amended hereby and he other Loan Documents remain in full force and effect.

      ss.8. Execution in Counterparts. This Amendment may be executed in any
number of counterparts and by each party on a separate counterpart, each of
which when so executed and delivered shall be an original, but all of which
together shall constitute one instrument. In proving this Amendment, it shall
not be necessary to produce or account for more than one such counterpart signed
by the party against whom enforcement is sought.

      ss.9. Miscellaneous. This Amendment shall be deemed to be a contract under
seal under the laws of The Commonwealth of Massachusetts and shall for all
purposes be construed in accordance with and governed by the laws of The
Commonwealth of Massachusetts. The captions in this Amendment are for
convenience of reference only and shall not define or limit the provisions
hereof. The Borrowers agree to pay to the Agent, on demand by the Agent, all
reasonable out-of-pocket costs and expenses incurred or sustained by the Agent
in connection with the preparation of this Amendment, including reasonable legal
fees.
<PAGE>

                                       -7-


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

                                        GRIFFITH CONSUMERS COMPANY


                                        By: /s/ [ILLEGIBLE]
                                           -------------------------------------
                                         Title: V-P Finance, Sec & Treasurer

                                        CARL KING, INC.


                                        By: /s/ [ILLEGIBLE]
                                           -------------------------------------
                                        Title: V-P

                                        SHORE STOP CORPORATION


                                        By: /s/ [ILLEGIBLE]
                                           -------------------------------------
                                        Title: V-P

                                        BANKBOSTON, N.A.
                                        f/k/a The First National Bank of Boston,
                                              individually and as Agent


                                        By:
                                           -------------------------------------
                                        Title:

                                        THE TRAVELERS INSURANCE COMPANY


                                        By:
                                           -------------------------------------
                                        Title:

                                        THE TRAVELERS INDEMNITY COMPANY


                                        By:
                                           -------------------------------------
                                        Title:

                                        SENIOR DEBT PORTFOLIO

                                        By: Boston Management and Research,
                                            as Investment Adviser


                                        By:
                                           -------------------------------------
                                        Title:
<PAGE>

                                       -7-


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

                                        GRIFFITH CONSUMERS COMPANY


                                        By:
                                           -------------------------------------
                                         Title:

                                        CARL KING, INC.


                                        By:
                                           -------------------------------------
                                        Title:

                                        SHORE STOP CORPORATION


                                        By:
                                           -------------------------------------
                                        Title:

                                        BANKBOSTON, N.A.
                                        f/k/a The First National Bank of Boston,
                                              individually and as Agent


                                        By: /s/ [ILLEGIBLE]
                                           -------------------------------------
                                        Title: Vice President

                                        THE TRAVELERS INSURANCE COMPANY


                                        By:
                                           -------------------------------------
                                        Title:

                                        THE TRAVELERS INDEMNITY COMPANY


                                        By:
                                           -------------------------------------
                                        Title:

                                        SENIOR DEBT PORTFOLIO

                                        By: Boston Management and Research,
                                            as Investment Adviser


                                        By:
                                           -------------------------------------
                                        Title:
<PAGE>

                                       -7-


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

                                        GRIFFITH CONSUMERS COMPANY


                                        By:
                                           -------------------------------------
                                         Title:

                                        CARL KING, INC.


                                        By:
                                           -------------------------------------
                                        Title:

                                        SHORE STOP CORPORATION


                                        By:
                                           -------------------------------------
                                        Title:

                                        BANKBOSTON, N.A.
                                        f/k/a The First National Bank of Boston,
                                              individually and as Agent


                                        By:
                                           -------------------------------------
                                        Title:

                                        THE TRAVELERS INSURANCE COMPANY


                                        By: /s/ Allen R. Cantrell
                                           -------------------------------------
                                        Title: Allen R. Cantrell
                                               Investment Officer

                                        THE TRAVELERS INDEMNITY COMPANY


                                        By: /s/ Allen R. Cantrell
                                           -------------------------------------
                                        Title: Allen R. Cantrell
                                               Investment Officer

                                        SENIOR DEBT PORTFOLIO

                                        By: Boston Management and Research,
                                            as Investment Adviser


                                        By:
                                           -------------------------------------
                                        Title:
<PAGE>

                                       -7-


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

                                        GRIFFITH CONSUMERS COMPANY


                                        By:
                                           -------------------------------------
                                         Title:

                                        CARL KING, INC.


                                        By:
                                           -------------------------------------
                                        Title:

                                        SHORE STOP CORPORATION


                                        By:
                                           -------------------------------------
                                        Title:

                                        BANKBOSTON, N.A.
                                        f/k/a The First National Bank of Boston,
                                              individually and as Agent


                                        By:
                                           -------------------------------------
                                        Title:

                                        THE TRAVELERS INSURANCE COMPANY


                                        By:
                                           -------------------------------------
                                        Title:

                                        THE TRAVELERS INDEMNITY COMPANY


                                        By:
                                           -------------------------------------
                                        Title:

                                        SENIOR DEBT PORTFOLIO

                                        By: Boston Management and Research,
                                            as Investment Adviser


                                        By: /s/ [ILLEGIBLE]
                                           -------------------------------------
                                        Title: Vice President
<PAGE>

                                       -8-


                                        RIGGS BANK N.A.

                                        By: /s/ [ILLEGIBLE]
                                           -------------------------------------
                                        Title: Vice President