<PAGE>   1
                                                                     EXHIBIT 4.5

      FIRST AMENDMENT dated as of September 12, 1997 (the "First Amendment") to
the NOTE AGREEMENT dated as of April 12, 1995 (the "Agreement") by and among
AMERIGAS PROPANE, L.P., a Delaware limited partnership (the "Company"), AMERIGAS
PROPANE, INC., a Pennsylvania corporation formerly known as New AmeriGas
Propane, Inc. (the "General Partner"), PETROLANE INCORPORATED, a Pennsylvania
corporation and successor by merger to Petrolane Incorporated, a California
corporation ("Petrolane"; the Company, the General Partner and Petrolane being
hereinafter collectively referred to as the "Obligors"), and each of the
noteholders listed in Schedule I to the Agreement as amended hereby (the
"holders").

      WHEREAS, the parties hereto desire to amend the Agreement as set forth
below;

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
set forth herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows.

            1.    Amendments to the Agreement.  Effective as of the Effective
Date (as hereinafter defined), the Agreement is hereby amended as follows:

            1.1.  Amendments to Section 10.1.

                  (a) Section 10.1 of the Agreement is hereby amended by
deleting the first sentence thereof in its entirety and by inserting in lieu
thereof the following new sentence:

                              "The Company will not permit the ratio of Total
                  Debt of the Company and its Restricted Subsidiaries to EBITDA
                  as at any fiscal quarter end to exceed 5.25 to 1.00. For
                  purposes of determining compliance with the ratio of Total
                  Debt to EBITDA, as set forth above, (A) EBITDA shall be
                  determined as at the end of each fiscal quarter for (I) the
                  four fiscal quarters then ended or (II) the eight fiscal
                  quarters then ended and divided by 2, whichever is greater,
                  and (B) Total Debt shall be determined as at the end of each
                  fiscal quarter."

                  (b)   Section 10.1(e) of the Agreement is hereby amended to
read in its entirety as follows:

                        "(e) The Company may become and remain liable with
                  respect to Indebtedness incurred for any purpose permitted by
                  the Revolving Credit Facility, and any Indebtedness incurred
                  for any such permitted purpose which replaces, extends,
                  renews, refunds or refinances any such Indebtedness, in whole
                  or in part, in an aggregate principal amount at any time not
                  in excess of $175,000,000 less the aggregate principal amount
                  outstanding under the Acquisition Facility;"

                  (c)   Section 10.1(f) of the Agreement is hereby amended to
read in its entirety as follows:

                        "(f) the Company may become and remain liable with
                  respect to Indebtedness, in addition to that otherwise
                  permitted by the foregoing subdivisions of this Section 10.1,
                  if on the date the Company becomes liable with respect to any
                  such additional Indebtedness and immediately after giving
<PAGE>   2
                  effect thereto and to the substantially concurrent repayment
                  of any other Indebtedness (i) the ratio of Consolidated Cash
                  Flow to Consolidated Pro Forma Debt Service is equal to or
                  greater than 2.50 to 1.0, (ii) the ratio of Consolidated Cash
                  Flow to Average Consolidated Pro Forma Debt Service is equal
                  to or greater than 1.25 to 1.0, and (iii) if such Indebtedness
                  is incurred other than for the purposes described in clause
                  (A) below, the Company would not be permitted to incur any
                  additional Indebtedness pursuant to Section 10.1(e) under the
                  Revolving Credit Facility or any extension, renewal,
                  refunding, replacement or refinancing thereof; provided that
                  if such Indebtedness (A) is incurred by the Company (x) to
                  finance the making of expenditures for the improvement or
                  repair of (to the extent such improvements and repairs may be
                  capitalized on the books of the Company in accordance with
                  GAAP) or additions to (including additions by way of
                  acquisitions or capital contributions of businesses and
                  related assets) the General Collateral, or (y) by assumption
                  in connection with additions (including additions by way of
                  acquisitions or capital contributions of businesses and
                  related assets) to the General Collateral and (B) is to be
                  secured under the Security Documents as provided in Section
                  10.2(m), then the Company may become liable with respect to
                  any such additional Indebtedness only if the Company would not
                  be permitted to incur any additional Indebtedness under
                  Section 10.1(b);"

            1.2.  Amendment to Section 10.2(l).  Section 10.2(l) of the
Agreement is hereby amended by deleting the words "or the Special Purpose
Facility" from such Section.

            1.3. Amendments to Section 10.22. Section 10.22 of the Agreement is
hereby amended by deleting subsection (e) thereof in its entirety and by
redesignating subsection (f) thereof (and any internal references thereto) as
subsection (e) thereof.

            1.4.  Amendment to Section 13.1.

                  (a) Section 13.1 of the Agreement is hereby amended by
deleting the definition of "Consolidated Adjusted Gross Worth" in its entirety.

                  (b) Section 13.1 of the Agreement is hereby amended further by
deleting the definition of "Consolidated Gross Worth" in its entirety.

                  (c) Section 13.1 of the Agreement is hereby amended further by
adding thereto the following additional defined terms in alphabetical order:

      EBIT means, for any period, the Company's and its Restricted Subsidiaries'
consolidated net income (not including extraordinary gains or losses) plus
interest charges and income tax expense in each case for such period, as
determined in accordance with GAAP.

      EBITDA means, for any period, EBIT plus the Company's and its Restricted
Subsidiaries' depreciation and amortization of property, plant and equipment and
intangible assets, in each case as taken into account in calculating
Consolidated Net Income, in each case for such period, as determined in
accordance with GAAP.


                                      -2-
<PAGE>   3
      For the purpose of calculating EBITDA for any period (the "Applicable
Period"), EBITDA shall be adjusted by the addition of the EBITDA of any Asset
Acquisitions made during the Applicable Period, as if such Asset Acquisitions
occurred on the first day of the Applicable Period plus the addition of the
"Savings Factor".

      The "Savings Factor" shall equal, with respect to any Asset Acquisition,
an amount equal to 50% of the difference between (a) Actual Acquisition Expense
minus (b) Pro Forma Acquisition Expense. "Actual Acquisition Expense" means an
amount equal to the personnel expenses and non personnel costs and expenses
(which would be deducted from gross profits in calculating costs and EBITDA)
related to the operation of any Asset Acquisition from the beginning of the
Applicable Period to the date of the purchase of the Asset Acquisition. "Pro
Forma Acquisition Expense" means an amount equal to the personnel and non
personnel costs and expenses (which would be deducted from gross profits in
calculating costs and EBITDA) that would have been incurred with respect to the
operation of any Asset Acquisition for the period from the beginning of the
Applicable Period to the date of purchase of the Asset Acquisition, on the
assumption that the ongoing personnel and non personnel cost and expense savings
realized as of the date of the Asset Acquisition had been realized on the first
day of the Applicable Period. In no event shall the aggregate Savings Factor for
any Applicable Period exceed 10% of EBITDA for the Company and its Restricted
Subsidiaries for such Applicable Period.

                  (d) Section 13.1 of the Agreement is hereby further amended by
deleting from the defined term "Credit Agreement" the words "and the Special
Purpose Facility", and by inserting the word "and" in lieu of the comma
immediately prior to the words "the Revolving Credit Facility."

            2. Conditions to Effectiveness of this First Amendment. This First
Amendment shall become effective only upon the satisfaction in full (or waiver
by the Required Holders) of the following conditions precedent (the first date
upon which each such condition shall have been so satisfied or waived being
herein referred to as the "Effective Date"):

                  (a)   No Defaults.  On the Effective Date (after giving
effect to this First Amendment), no Default or Event of Default shall have
occurred and be continuing.

                  (b) Credit Agreement. The Credit Agreement shall have been
amended to delete the first sentence of Section 8.1 thereof and by adding a
covenant thereto substantially the same as the covenant added as Section 10.1(i)
of the Agreement by this First Amendment. The covenants and events of default
set forth in the Credit Agreement shall not have been otherwise amended in any
material respect.

                  (c) First Amendment. Each of the Obligors and the Required
Holders shall have executed this First Amendment, and counterparts hereof
bearing the signatures of the Obligors shall have been delivered to the holders
together with a notice from the Company to each holder as to the satisfaction of
this condition and the condition specified in clause (b) of this Section 2.

                  (d) Fees. Without limiting the provisions of Section 16.1 of
the Agreement, special counsel to the holders shall have received its reasonable
fees, charges and disbursements to the extent reflected in a statement of such
special counsel rendered to the Company.


                                      -3-
<PAGE>   4
            3. Agreement; Terms. Except as expressly amended hereby, the
Agreement shall continue in full force and effect in accordance with the
provisions thereof on the date hereof, and this First Amendment shall not be
deemed to waive or amend any provision of the Agreement except as expressly set
forth herein. As used in the Agreement, the terms "this Agreement," "herein,"
"hereinafter," "hereunder," "hereto" and words of similar import shall mean and
refer to, from and after the Effective Date, unless the context otherwise
specifically requires, the Agreement as amended by this First Amendment.
Capitalized terms used and not defined herein shall have the meanings assigned
to such terms in the Agreement.

            4.  Headings.  Section headings in this First Amendment are
included herein for convenience of reference only and shall not define, limit
or otherwise affect any of the terms or provisions hereof.

            5. Counterparts. This First Amendment may be executed by the parties
hereto in separate counterparts, each of which when so executed and delivered
shall be an original, but all such counterparts shall together constitute one
and the same instrument, and all signatures need not appear on any one
counterpart.

            6. Expenses. The Company agrees to pay all reasonable out-of-pocket
expenses incurred by the holders in connection with the preparation of this
First Amendment, including, but not limited to, the reasonable fees, charges and
disbursements of counsel for the holders as provided for in Section 16.1 of the
Agreement.

            7.  Governing Law.  This First Amendment shall be governed by,
and construed in accordance with, the laws of the State of New York (other
than any conflicts of law rule which might result in the application of the
laws of any other jurisdiction).

            8. Ratification and Confirmation of Security Documents.  The
Company hereby ratifies and confirms the provisions of the Security Documents
for the benefit from time to time of the holders of the Notes.


                                      -4-
<PAGE>   5
            IN WITNESS WHEREOF, the parties hereto have caused this First
Amendment to be executed as of the date first above written.

                                    AMERIGAS PROPANE, L.P.


                                    By:  AmeriGas Propane, Inc.,
                                         its general partner


                                    By:  s/Charles L. Ladner
                                         --------------------------------------
                                         Charles L. Ladner
                                         Vice President - Finance and
                                         Accounting


                                    AMERIGAS PROPANE, INC.


                                    By:  s/Charles L. Ladner
                                         --------------------------------------
                                         Charles L. Ladner
                                         Vice President - Finance and
                                         Accounting


                                    PETROLANE INCORPORATED


                                    By:  s/Brendan P. Bovaird
                                         --------------------------------------
                                         Brendan P. Bovaird
                                         Vice President


                                    THE PRUDENTIAL INSURANCE COMPANY OF
                                     AMERICA


                                    By:  s/Robert G. Gwin
                                         --------------------------------------
                                         Robert G. Gwin
                                         Vice President


                                    PRUCO LIFE INSURANCE COMPANY


                                    By:  s/Randall M. Kob
                                         --------------------------------------
                                         Randall M. Kob
                                         Vice President


                                    METROPOLITAN LIFE INSURANCE COMPANY


                                    By:  s/James A. Wiviott
                                         --------------------------------------
                                         James A. Wiviott
                                         Assistant Vice President


                                      -5-
<PAGE>   6
                                    THE EQUITABLE LIFE INSURANCE SOCIETY OF
                                    THE UNITED STATES


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


                                    CONNECTICUT GENERAL LIFE INSURANCE COMPANY


                                    By:  CIGNA INVESTMENTS, INC.


                                    By:  s/James G. Schelling
                                         --------------------------------------
                                         James G. Schelling
                                         Managing Director


                                    CIGNA PROPERTY AND CASUALTY INSURANCE
                                    COMPANY


                                    By:  CIGNA INVESTMENTS, INC.


                                    By:  s/James G. Schelling
                                         --------------------------------------
                                         James G. Schelling
                                         Managing Director


                                    CENTURY INDEMNITY COMPANY


                                    By:  CIGNA INVESTMENTS, INC.


                                    By:  s/James G. Schelling
                                         --------------------------------------
                                         James G. Schelling
                                         Managing Director


                                    LIFE INSURANCE COMPANY OF NORTH AMERICA


                                    By:  CIGNA INVESTMENTS, INC.


                                    By:  s/James G. Schelling
                                         --------------------------------------
                                         James G. Schelling
                                         Managing Director


                                      -6-
<PAGE>   7
                                    TEACHERS INSURANCE AND ANNUITY
                                    ASSOCIATION OF AMERICA


                                    By:  s/Thomas E. Solano
                                         --------------------------------------
                                         Thomas E. Solano
                                         Director Private Placements


                                    THE TRAVELERS INSURANCE COMPANY


                                    By:  s/Robert M. Mills
                                         --------------------------------------
                                         Robert M. Mills
                                         Investment Officer


                                      -7-