<PAGE>

                                                                   Exhibit 10(g)

                               SECOND AMENDMENT
                               ----------------


     THIS SECOND AMENDMENT dated as of July 14, 1999 (this "Amendment") amends
the Credit Agreement dated as of September 29, 1998 (as previously amended, the
"Credit Agreement") among United Rentals (North America), Inc. (the "Company"),
United Rentals, Inc. ("Parent"), United Rentals of Canada, Inc., various
financial institutions, Bank of America Canada, as Canadian Agent, and Bank of
America National Trust and Savings Association, as U.S. Agent.  Terms defined in
the Credit Agreement are, unless otherwise defined herein or the context
otherwise requires, used herein as defined therein.

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

     NOW, THEREFORE, the parties hereto agree as follows:

     SECTION 1  Amendments.  Effective on (and subject to the occurrence of) the
                ----------
Amendment Effective Date (as defined below), the Credit Agreement shall be
amended as set forth in this Section 1.
                             ---------

     1.1  Definition of Business Day.  The definition of "Business Day" in
          --------------------------
Section 1.1 is amended by inserting "Charlotte," immediately before "Chicago"
therein.

     1.2  Definition of Funded Debt.  The definition of "Funded Debt" in Section
          -------------------------
1.1 is amended in its entirety to read as follows:

          Funded Debt means (a) all Debt of Parent and its Subsidiaries and
          -----------
     (b) to the extent not included in the definition of Debt, the aggregate
     outstanding investment or claim held at such time by purchasers, assignees
     or other transferees of (or of interests in) receivables or other rights to
     payment of Parent and its Subsidiaries in connection with any
     Securitization Transaction (regardless of the accounting treatment of such
     Securitization Transaction), but excluding (i) contingent obligations in
     respect of undrawn letters of credit and Suretyship Liabilities (except to
     the extent constituting contingent obligations or Suretyship Liabilities in
     respect of Funded Debt of a Person other than Parent or any Subsidiary),
     (ii) Hedging Obligations, (iii) Debt of the Company to Subsidiaries and
     Debt of Subsidiaries to the Company or to other Subsidiaries and (iv) Debt
     (including guaranties thereof) in respect of the QuIPS Debentures and the
     QuIPS Preferred Securities.

     1.3  Definition of Interest Expense.  The definition of "Interest
          ------------------------------
Expense" in Section 1.1 is amended in its entirety to read as follows:

          Interest Expense means for any period the sum, without duplication, of
          ----------------
     (a) the consolidated interest expense of Parent and its Subsidiaries for
     such period (including,
<PAGE>

     without duplication, interest paid on the QuIPS Debentures, distributions
     on (but not redemptions of) the QuIPS Preferred Securities, imputed
     interest on Capital Leases and any interest which is capitalized but
     excluding amortization of deferred financing costs) and (b) consolidated
     yield or discount accrued during such period on the aggregate investment or
     claim held by purchasers, assignees or other transferees of, or of
     interests in, accounts receivable, lease receivables and other rights to
     payment of Parent and its Subsidiaries in connection with any
     Securitization Transaction (regardless of the accounting treatment of such
     Securitization Transaction).

     1.4  Definition of Investment.  The definition of "Investment" in Section
          ------------------------
1.1 is amended by deleting "the Company" therein and substituting "Parent"
therefor.

     1.5  Definition of Permitted Senior Secured Debt.  The definition of
          -------------------------------------------
"Permitted Senior Secured Debt" in Section 1.1 is amended in its entirety to
read as follows:

          Permitted Senior Secured Debt means any Debt arising under (a) the
          -----------------------------
     Term Loan Agreement dated as of July 15, 1999 among Parent, the Company,
     various financial institutions and BofA, as Agent; and (b) any other term
     loan agreement (other than the Term Loan Agreement as defined herein) among
     Parent, the Company, various financial institutions and BofA, as agent;

     provided that (i) any such other term loan agreement shall contain
     --------
     covenants and defaults which are no more restrictive for Parent and its
     Subsidiaries than the covenants and defaults contained in this Agreement,
     (ii) any such Debt shall mature no earlier than September 30, 2005 and
     shall have amortization of no more than 20% of the principal amount thereof
     prior to July 15, 2005, (iii) any such Debt shall constitute "Senior
     Indebtedness" as defined in each Subordinated Note Indenture and (iv) no
     Debt under any such other term loan agreement shall have interest rate
     spreads greater than (x) if such Debt matures on or before December 31,
     2005, the then-applicable interest rate spreads under the Term Loan
     Agreement (as defined herein) or (y) if such Debt matures after December
     31, 2005, the then-applicable interest rate spreads under the Term Loan
     Agreement referred to in clause (a) above.
                              ----------

     1.6  Definition of Reference Rate.  The definition of "Reference Rate" in
          ----------------------------
Section 1.1 is amended by inserting the following immediately after "California"
in the second line thereof: "(or such other office in the United States of
America as BofA shall specify from time to time)".

     1.7  Definition of Seller Subordinated Debt.  The definition of "Seller
          --------------------------------------
Subordinated Debt" in Section 1.1 is amended by deleting the reference to

"Section 10.11(d)" therein and substituting "Section 10.11(c)" therefor.
-----------------                            ----------------

     1.8  Definition of Subordinated Debt.  The definition of "Subordinated
          -------------------------------
Debt" in Section 1.1 is amended in its entirety to read as follows:

                                       2
<PAGE>

            Subordinated Debt means (a) the U.S.$200,000,000 of 9.50% unsecured
            -----------------
     senior subordinated notes due 2008 issued by the Company (then known as
     United Rentals, Inc.) on May 22, 1998 and the unsecured subordinated
     guarantees thereof provided for in the applicable  Subordinated Note
     Indenture, (b) the U.S.$205,000,000 of 8.80% unsecured senior subordinated
     notes due 2008 issued by the Company on August 12, 1998 and the unsecured
     subordinated guarantees thereof provided for in the applicable Subordinated
     Note Indenture, (c) the U.S.$300,000,000 of 9.25% unsecured senior
     subordinated notes due 2009 issued by the Company on December 15, 1998 and
     the unsecured subordinated guarantees thereof provided for in the
     applicable Subordinated Note Indenture, (d) the U.S.$250,000,000 of 9.0%
     unsecured senior subordinated notes due 2009 issued by the Company on March
     23, 1999 and the unsecured subordinated guarantees thereof provided for in
     the applicable Subordinated Note Indenture, (e) Seller Subordinated Debt
     and (f) any other unsecured Debt of the Company and unsecured guarantees
     thereof by any Subsidiary of the Company which (i) is owed to Persons other
     than officers, employees, directors or Affiliates of the Company, (ii) has
     no amortization prior to December 31, 2006 and (iii) has subordination
     terms (including subordination terms with respect to guarantees) which are
     not less favorable to the Banks than those set forth in the Subordinated
     Note Indentures or are otherwise approved by the Required Banks, such
     approval not to be unreasonably withheld.

     1.9  Definition of Subordinated Note Indenture.  The definition of
          -----------------------------------------
"Subordinated Note Indenture" in Section 1.1 is amended in its entirety to read
as follows:

          Subordinated Note Indenture means each of (a) the Indenture dated as
          ---------------------------
     of May 22, 1998 among the Company (then known as United Rentals, Inc.),
     various Subsidiaries of the Company and State Street Bank and Trust
     Company, as Trustee, pursuant to which the Company issued U.S.$200,000,000
     of Subordinated Debt, (b) the Indenture dated as August 12, 1998 among the
     Company, various Subsidiaries of the Company and State Street Bank and
     Trust Company, as Trustee, pursuant to which the Company issued
     U.S.$205,000,000 of Subordinated Debt, (c) the Indenture dated as of
     December 15, 1998 among the Company, various Subsidiaries of the Company
     and State Street Bank and Trust Company, as Trustee, pursuant to which the
     Company issued U.S.$300,000,000 of Subordinated Debt, and (d) the Indenture
     dated as of March 23, 1999 among the Company, various Subsidiaries of the
     Company and The Bank of New York, as Trustee, pursuant to which the Company
     issued U.S.$250,000,000 of Subordinated Debt.

     1.10 Definition of Vendor Financing Arrangement.  The definition of "Vendor
          ------------------------------------------
Financing Arrangement" in Section 1.1 is amended by deleting the references to
"the Company" therein and substituting "Parent" therefor.

                                       3
<PAGE>

     1.11 Addition of Definitions.  The following definitions are added to
          -----------------------
Section 1.1 in appropriate alphabetical sequence:

          Securitization Transaction means any sale, assignment or other
          --------------------------
     transfer by Parent or any Subsidiary of accounts receivable, lease
     receivables or other payment obligations owing to Parent or such Subsidiary
     or any interest in any of the foregoing, together in each case with any
     collections and other proceeds thereof, any collection or deposit accounts
     related thereto, and any collateral, guaranties or other property or claims
     supporting or securing payment by the obligor thereon of, or otherwise
     related to, or subject to leases giving rise to, any such receivables.

          Special Purpose Vehicle means a trust, bankruptcy remote entity or
          -----------------------
     other special purpose entity which is a Subsidiary of Parent (or, if not a
     Subsidiary, the common equity of which is wholly-owned, directly or
     indirectly, by Parent) and which is formed for the purpose of, and engages
     in no material business other than, acting as an issuer or a depositor in a
     Securitization Transaction (and, in connection therewith, owning accounts
     receivable, lease receivables, other rights to payment, leases and related
     assets and pledging or transferring any of the foregoing or interests
     therein).

     1.12 Amendment to Section 10.6.4.  Section 10.6.4 is amended in its
          ---------------------------
entirety to read as follows:

          10.6.4  Senior Debt to Tangible Assets.  Not permit the ratio of (i)
                  ------------------------------
     Senior Debt to (ii) the sum of Tangible Assets plus the outstanding amount
     of accounts receivable, lease receivables and other payment obligations
     which are not included on Parent's consolidated balance sheet but would be
     so included if not sold pursuant to a Securitization Transaction to exceed
     1.0 to 1.0 at any time.

     1.13 Amendment to Section 10.7.  Section 10.7 is amended in its entirety to
          -------------------------
read as follows:

          10.7  Limitations on Debt.  Not, and not permit any Subsidiary to,
                -------------------
     create, incur, assume or suffer to exist any Debt, except:

          (a)   obligations hereunder, under the other Loan Documents, under the
          Term Loan Agreement and under the other "Loan Documents" as defined in
          the Term Loan Agreement;

          (b)   unsecured Debt of Parent, the Company and Subsidiaries of the
          Company (excluding Contingent Payments and Seller Subordinated Debt);
          provided that no Subsidiary shall incur any such Debt if, after giving
          --------
          effect thereto, the aggregate amount of all then-outstanding Debt of
          Subsidiaries


                                       4
<PAGE>

          of the Company permitted solely by this clause (b) would
                                                  ----------
          exceed 10% of Net Worth;

          (c) Debt of Parent or any Subsidiary in respect of Capital Leases or
          arising in connection with the acquisition of equipment (including
          Debt assumed in connection with an asset purchase permitted by Section
                                                                         -------
          10.11, or incurred pursuant to a Capital Lease or in connection with
          -----
          the acquisition of equipment by a Person before it became a Subsidiary
          in connection with a stock purchase permitted by Section 10.11, in
                                                           -------------
          each case so long as such Debt is not incurred in contemplation of
          such purchase), and refinancings of any such Debt so long as the terms
          applicable to such refinanced Debt are no less favorable to Parent or
          the applicable Subsidiary than the terms in effect immediately prior
          to such refinancing, provided that the aggregate amount of all such
                               --------
          Debt at any time outstanding shall not exceed a Dollar Equivalent
          amount equal to U.S.$150,000,000;

          (d) Debt of Subsidiaries owed to the Company or Parent; provided that
                                                                  --------
          the aggregate amount of all such Debt of Foreign Subsidiaries owed to
          the Company and Parent shall not at any time exceed 15% of the
          consolidated assets of Parent and its Subsidiaries;

          (e) unsecured Debt of the Company to Subsidiaries of the Company, of
          Parent to the Company and Subsidiaries of the Company and of any
          Special Purpose Vehicle to any Subsidiary of the Company;

          (f) Subordinated Debt; provided that (i) the aggregate principal
                                 --------
          amount of all Seller Subordinated Debt at any time outstanding shall
          not exceed a Dollar Equivalent amount of U.S.$50,000,000 and (ii) the
          Company shall not issue or incur any Debt described in clause (f) of
                                                                 ----------
          the definition of Subordinated Debt (x) at any time that an Event of
          Default or Unmatured Event of Default exists or would result therefrom
          and (y) unless the Company has delivered to the U.S. Agent (which
          shall promptly deliver a copy thereof to each U.S. Bank) a certificate
          in reasonable detail demonstrating that, after giving effect to such
          issuance or incurrence, Parent will be in pro forma compliance with
          all financial covenants set forth in this Section 10;
                                                    ----------

          (g) other Debt of the Company or any Subsidiary, not of a type
          described in clause (c), outstanding on the date hereof and listed in
                       ----------
          Schedule 10.7(g);
          ----------------

                                       5
<PAGE>

          (h) Contingent Payments, provided that Parent shall not, and shall not
                                   --------
          permit any Subsidiary to, incur any obligation to make Contingent
          Payments the maximum possible amount of which exceeds a Dollar
          Equivalent amount of U.S.$50,000,000 in the aggregate for all
          Contingent Payments at any time outstanding;

          (i) the QuIPS Debentures, the QuIPS Preferred Securities and the QuIPS
          Guarantees;

          (j) Permitted Senior Secured Debt and guarantees thereof, provided
                                                                    --------
          that the aggregate principal amount of all Permitted Senior Secured
          Debt shall not at any time exceed U.S.$750,000,000;

          (k) Guarantees by Parent of the obligations of the Company or any
          Subsidiary; provided that any such guaranty of Debt is subordinated to
          the obligations of Parent under the Parent Guaranty at least to the
          extent set forth in Exhibit G or otherwise in a manner reasonably
                              ---------
          satisfactory to the Required Banks;

          (l) unsecured recourse obligations of Parent or any Subsidiary in
          respect of Vendor Financing Arrangements;

          (m) Hedging Obligations incurred for purposes of protection from
          price, interest rate or currency fluctuations posed by bona fide debt,
          contract or purchase order obligations or from changes in the price of
          Parent's stock; and

          (n) Debt in connection with Securitization Transactions; provided that
                                                                   --------
          the aggregate principal amount of all such Debt shall not at any time
          exceed U.S.$150,000,000.

          For purposes of clause (h) above, a Contingent Payment shall be deemed
                          ----------
     to be "outstanding" from the time that Parent or any Subsidiary enters into
     the agreement containing the obligation to make such Contingent Payment
     until such time as either such Contingent Payment has been made in full or
     it has become certain that such Contingent Payment will never have to be
     made.

     1.14 Amendment to Section 10.8.  Section 10.8 is amended by (a) immediately
          -------------------------
following the last reference to "Debt" in clause (d) thereof adding the
following "and the proceeds (including insurance proceeds) of any disposition or
loss of such property", (b) deleting the word "and" immediately after the
semicolon in clause (f) thereof, (c) deleting the period at the end of

                                       6
<PAGE>

clause (g) thereof and substituting a semicolon and the word "and" therefor and
(d) adding the following new clause (h):

          (h) Liens arising in connection with Securitization Transactions;
          provided that the aggregate investment or claim held at any time by
          --------
          all purchasers, assignees or other transferees of (or of interests in)
          accounts receivable, lease receivables and other rights to payment in
          all Securitization Transactions shall not exceed $150,000,000.

     1.15 Amendment to Section 10.10.  Section 10.10 is amended by (a) deleting
          --------------------------
the word "its" in clause (f)(ii) thereof and substituting the word "the"
therefor, (b) adding the following immediately after the parenthetical in clause
(f)(ii) thereof:  "of Parent, any Acquisition Subsidiary, the QuIPS Trust and
any Special Purpose Vehicle" and (c) adding the following sentence to the end of
such section:  "Nothing in this Section 10.10 shall prohibit Parent from
permitting the cashless exercise of any options or warrants for stock of
Parent."

     1.16 Amendment to Section 10.11.  Section 10.11 is amended in its entirety
          --------------------------
to read as follows:

          10.11  Mergers, Consolidations, Amalgamations, Sales.  Not, and not
                 ---------------------------------------------
     permit any Subsidiary to, be a party to any merger, consolidation or
     amalgamation, or purchase or otherwise acquire all or substantially all of
     the assets or any stock of any class of, or any partnership or joint
     venture interest in, any other Person, or, except in the ordinary course of
     its business (including sales of equipment consistent with industry
     practice), sell, transfer, convey or lease all or any substantial part of
     its assets, or sell or assign with or without recourse any receivables,
     except for (a) any such merger or consolidation, amalgamation, sale,
     transfer, conveyance, lease or assignment of or by any wholly-owned
     Subsidiary of the Company into the Company or into, with or to any other
     wholly-owned Subsidiary of the Company; (b) any such purchase or other
     acquisition by the Company or any wholly-owned Subsidiary of the Company of
     the assets or stock of any wholly-owned Subsidiary of the Company; (c) any
     such purchase or other acquisition (including pursuant to a merger) by
     Parent, an Acquisition Subsidiary, the Company or any wholly-owned
     Subsidiary of the Company of the assets or stock of any other Person where
     (1) such assets (in the case of an asset purchase) are for use, or such
     Person (in the case of a stock purchase) is engaged, solely in the
     equipment rental and related businesses; (2) immediately before and after
     giving effect to such purchase or acquisition, no Event of Default or
     Unmatured Event of Default shall have occurred and be continuing;  (3) the
     board of directors of such Person has not announced that it will oppose
     such acquisition and has not commenced any litigation which alleges that
     such acquisition violates or will violate

                                       7
<PAGE>

     any requirement of law or any contractual obligation of such Person; (4) in
     the case of any such purchase or other acquisition by Parent or any
     Acquisition Subsidiary, Parent immediately contributes the acquired stock
     or assets to the Company or merges the acquired company or the Acquisition
     Subsidiary into the Company or with or into any wholly-owned Subsidiary of
     the Company; and (5) either (i) the aggregate consideration to be paid by
     Parent and its Subsidiaries (including any Debt assumed or issued in
     connection therewith, the amount thereof to be calculated in accordance
     with GAAP, but excluding any capital stock of or other equity interest in
     Parent which is part of such consideration) in connection with such
     purchase or other acquisition (or any series of related acquisitions) is
     less than a Dollar Equivalent amount of U.S.$150,000,000 or (ii) (x) Parent
     is in pro forma compliance with all the financial ratios and restrictions
     set forth in Section 10.6 and (y) the Required Banks have consented to such
                  ------------
     purchase or acquisition; (d) the sale, assignment or other transfer of
     accounts receivable, lease receivables or other rights to payment pursuant
     to any Securitization Transaction; provided that the aggregate investment
     or claim held at any time by all purchasers, assignees or other transferees
     of (or of interests in) such receivables or other rights to payment shall
     not exceed $150,000,000; and (e) sales and dispositions of assets
     (including the stock of Subsidiaries), in addition to sales and other
     dispositions permitted by clause (d), so long as the net book value of all
     assets sold or otherwise disposed of in any Fiscal Year does not exceed 5%
     of the net book value of the consolidated assets of Parent and its
     Subsidiaries as of the last day of the preceding Fiscal Year.

     1.17 Amendment to Section 10.14.  Section 10.14 is amended in its entirety
          --------------------------
to read as follows:

          10.14  Further Assurances.  Take, and cause each Subsidiary to take,
                 ------------------
     such actions as are necessary or as either Agent or the Required Banks may
     reasonably request from time to time (including the execution and delivery
     of guaranties, security agreements, pledge agreements, financing statements
     and other documents, the filing or recording of any of the foregoing, and
     the delivery of stock certificates and other collateral with respect to
     which perfection is obtained by possession) to ensure that (i) the
     obligations of the Company hereunder and under the other Loan Documents are
     secured by substantially all of the assets (other than real property and
     the Company's interest in any Special Purpose Vehicle) of the Company and
     guaranteed by Parent by execution of the Parent Guaranty and by all of the
     U.S. Subsidiaries (including, promptly upon the acquisition or creation
     thereof, any U.S. Subsidiary acquired or created after the date hereof) by
     execution of a counterpart of the U.S. Guaranty (provided that neither the
     QuIPS Trust nor any Special Purpose Vehicle shall have any obligation to
     execute the

                                       8
<PAGE>

     U.S. Guaranty), (ii) the obligations of Parent under the Parent Guaranty
     are secured by substantially all of the assets of Parent (other than
     Parent's interest in the QuIPS Trust or any Special Purpose Vehicle), (iii)
     the obligations of each U.S. Subsidiary (other than the QuIPS Trust and any
     Special Purpose Vehicle) under the U.S. Guaranty are secured by
     substantially all of the assets (other than real property and such U.S.
     Subsidiary's interest in any Special Purpose Vehicle) of such U.S.
     Subsidiary, (iv) the obligations of UR Canada hereunder and under the other
     Loan Documents are secured by substantially all of the assets (other than
     real property) of UR Canada and guaranteed by all of the Canadian
     Subsidiaries (including, promptly upon the acquisition or creation thereof,
     any Canadian Subsidiary acquired or created after the date hereof) by
     execution of a Canadian Guaranty and (v) the obligations of each Canadian
     Subsidiary under its Canadian Guaranty are secured by substantially all
     assets (other than real property) of such Canadian Subsidiary. In addition,
     upon the occurrence of any Event of Default or Unmatured Event of Default
     and the request of U.S. Banks having Percentages aggregating 80% or more,
     the Company will cause each Canadian Subsidiary to guaranty all of the
     obligations of the Company hereunder and to take all actions necessary so
     that the obligations of such Canadian Subsidiary under such guaranty are
     secured by substantially all of the assets (other than real property) of
     such Canadian Subsidiary (it being understood that, at the request of the
     Company at any time thereafter when no Event of Default or Unmatured Event
     of Default exists, such guaranties and collateral security shall be
     released).

     1.18 Amendment to Section 10.15.  Section 10.15 is amended in its entirety
          --------------------------
to read as follows:

          10.15  Transactions with Affiliates.  Not, and not permit any
                 ----------------------------
     Subsidiary to, enter into, or cause, suffer or permit to exist any
     transaction, arrangement or contract with any of its other Affiliates
     (other than Parent, the Company and Subsidiaries of the Company) which is
     on terms which are less favorable than are obtainable from any Person which
     is not one of its Affiliates; provided that Parent may enter into
     transactions with Acquisition Subsidiaries or the QuIPS Trust, and Parent
     or any Subsidiary may enter into transactions with any Special Purpose
     Vehicle in connection with any Securitization Transaction, to the extent
     permitted by the terms of this Agreement.

     1.19 Amendment to Section 10.18.  Section 10.18 is amended by deleting the
          --------------------------
reference to "the Company" therein and substituting "Parent" therefor.

                                       9
<PAGE>

     1.20 Amendment to Section 10.19.  Section 10.19 is amended by adding
          --------------------------
"(other than any Special Purpose Vehicle)" immediately after the second
reference to "the Company" in clause (b) thereof.

     1.21 Amendment to Section 10.20.  Section 10.20 is amended by adding
          --------------------------
"(other than the QuIPS Trust and any Special Purpose Vehicle)" immediately after
the reference to "Subsidiary" therein.

     1.22 Amendment to Section 10.21.  Section 10.21 is amended by (a) inserting
          --------------------------
", in Subsidiaries of the Company" immediately after the reference to "Company"
in clause (h) thereof, (b) deleting the word "and" at the end of clause (i)
thereof, (c) adding the word "and" at the end of clause (j) thereof, (c) adding
the following new clause (k):

          (k) Investments by Parent or any Subsidiary in any Special Purpose
          Vehicle; provided that the aggregate amount of all such Investments
                   --------
          made in cash shall not exceed $5,000,000;

and (d) deleting the language "or (g)" in clause (y) of the proviso thereto and
                                   -
substituting ", (g) or (k)" therefor.
                 -      -

     1.23 Amendment to Section 10.23.  Section 10.23 is amended in its entirety
          --------------------------
to read as follows:

          10.23  Activities of Parent.  Not engage in any business other than
                 --------------------
     ownership of the Company, Acquisition Subsidiaries, the QuIPS Trust and any
     Special Purpose Vehicle and activities reasonably related thereto
     (including the incurrence of Debt permitted by Section 10.7, the incurrence
                                                    ------------
     of unsecured trade obligations in respect of goods to be delivered to and
     properties to be used by, and services (including management and consulting
     services) to be performed for the benefit of, and unsecured lease
     obligations incurred for the benefit of, Subsidiaries and the incurrence of
     payroll and benefit expenses).  Without limiting the foregoing, Parent will
     not (a) incur any Debt other than the QuIPS Debentures, the QuIPS Preferred
     Securities, the Parent Guaranty, the QuIPS Guarantees, Debt permitted by

     Section 10.7 and guarantees of the obligations of the Company or any other
     ------------
     Subsidiary (provided that any such guaranty of Debt is subordinated to the
     obligations of Parent under the Parent Guaranty at least to the extent set
     forth in Exhibit G or otherwise in a manner reasonably satisfactory to the
              ---------
     Required Banks), (b) make any Investments other than (i) Investments in the
     Company and its Subsidiaries, (ii) Investments in Acquisition Subsidiaries,
     (iii) Investments in the QuIPS Trust existing on the date hereof and (iv)
     Investments in any Special Purpose Vehicle, (c) grant any Liens on any of
     its assets (other than pursuant to

                                      10
<PAGE>

     the U.S. Security Agreement or as permitted under this Agreement) or (d)
     permit any amendment to or modification of the QuIPS Debentures, the QuIPS
     Preferred Securities, either QuIPS Guarantee or the QuIPS Indenture which,
     in any such case, is adverse to the interests of the Banks.

     1.24  Amendment to Section 12.1.2.  Section 12.1.2 is amended by adding the
           ----------------------------
following  immediately before the period at the end thereof:

     ; or any event of default, default, liquidation event or similar event
     shall occur or exist relating to any Securitization Transaction if the
     effect of such event is to cause or permit (subject to any applicable grace
     period) an aggregate cash amount exceeding a Dollar Equivalent amount of
     U.S. $15,000,000 to become immediately due and payable by Parent or any
     Subsidiary under such Securitization Transaction

     1.25 Amendment to Section 12.1.11.  Section 12.1.11 is amended by deleting
          ----------------------------
the word "either" in clause (d) thereof and substituting the word "any"
therefor.

     1.26 Tax Forms.  The parenthetical clause "(or any applicable successor
          ---------
form)" is added in the following places: (a) after "Forms 1001 and W-8" in
subsection 13.10(a)(i); (b) after "Form 4224" in subsection 13.10(a)(ii); (c)
after "Form 1001" twice in subsection 13.10(b); and (d) after "Form 4224" in
Section 13.10(c).

     SECTION 2  Representations and Warranties.  Parent and the Company
                ------------------------------
represent and warrant to the Agents and the Banks that (a) each of the
representations and warranties made by Parent and the Company in Section 9
(excluding Section 9.8) of the Credit Agreement, as amended hereby (as so
amended, the "Amended Agreement"), is true and correct as of the date hereof,
with the same effect as if made on such date, (b) the execution and delivery
hereof by Parent and the Company, and the performance by Parent and the Company
of their respective obligations under the Amended Agreement and each other Loan
Document to which such entity is a party, (i) are within the powers of Parent
and the Company, (ii) have been duly authorized by all necessary corporate
action on the part of Parent and the Company, (iii) have received all necessary
governmental approvals and (iv) do not and will not contravene or conflict with
(A) any provision of law or the certificate of incorporation or by-laws or other
organizational documents of Parent or the Company or (B) any agreement,
judgment, injunction, order, decree or other instrument binding upon Parent, the
Company or any other Subsidiary of Parent, (c) the Amended Agreement and each
other Loan Document to which Parent or the Company is a party is the legal,
valid and binding obligation of Parent and the Company (as applicable),
enforceable against Parent and the Company (as applicable) in accordance with
its terms, except as enforceability may be limited by bankruptcy, insolvency or
other similar laws of general application affecting the enforcement of
creditors' rights or by general principles of equity limiting the availability
of equitable remedies and (d) no Event of Default or Unmatured Event of Default
has occurred or is continuing.

                                      11
<PAGE>

     SECTION 3  Effectiveness.  The amendments set forth in Section 1 above
                -------------                               ---------
shall become effective on the date (the "Amendment Effective Date") when the
U.S. Agent shall have received (a) for the account of each U.S. Bank which
delivers to the U.S. Agent an executed signature page hereto not later than 3:00
p.m. (Chicago time) on July 14, 1999, the amendment fee in the amount previously
agreed to between the Company and such Bank and (b) all of the following, in
form and substance satisfactory to the U.S. Agent:

     (i)   Counterparts hereof executed by the Company, Parent, the Required
Banks and the U.S. Agent.

    (ii)   Certified copies of resolutions of the Board of Directors of the
Company authorizing or ratifying the execution and delivery by the Company of
this Amendment and the performance by the Company of its obligations under the
Amended Agreement; and certified copies of resolutions of the Board of Directors
of Parent authorizing or ratifying the execution and delivery by Parent of this
Amendment and the performance by Parent of its obligations under the Amended
Agreement.

     (iii)  A certificate of the Secretary or an Assistant Secretary of each
of Parent and the Company certifying the names of the officer or officers of
such entity authorized to sign this Amendment, together with a sample of the
true signature of each such officer.

      (iv)  The opinions of (a) Weil, Gotshal & Manges LLP, special counsel to
Parent and the Company, and (b) Oscar D. Folger, counsel to Parent and the
Company.

      (v)   A Confirmation substantially in the form of Exhibit A signed by each
                                                       ---------
Loan Party.

     SECTION 4  Miscellaneous.
                -------------

     4.1  Continuing Effectiveness, etc. As herein amended, the Credit Agreement
          ------------------------------
shall remain in full force and effect and is hereby ratified and confirmed in
all respects.  After the Amendment Effective Date, all references in the Credit
Agreement and the other Loan Documents to the "Credit Agreement" or similar
terms shall refer to the Amended Agreement.

     4.2  Counterparts.  This Amendment may be executed in any number of
          ------------
counterparts and by the different parties on separate counterparts, and each
such counterpart shall be deemed to be an original but all such counterparts
shall together constitute one and the same agreement.

     4.3  Expenses.  The Company agrees to pay all reasonable expenses of the
          --------
U.S. Agent, including reasonable fees and charges of counsel for the U.S. Agent,
in connection with the preparation, execution and delivery of this Amendment.

                                      12
<PAGE>

     4.4  Governing Law.  This Amendment shall be construed in accordance with
          -------------
and governed by the substantive laws of the State of Illinois applicable to
contracts made and to be performed entirely within such State.

     4.5  Successors and Assigns.  This Amendment shall be binding upon Parent,
          ----------------------
the Company, the Banks and the Agents and their respective successors and
assigns, and shall inure to the benefit of Parent, the Company, the Banks and
the Agents and the respective successors and assigns of the Banks and the
Agents.

                                      13
<PAGE>

     Delivered at Chicago, Illinois, as of the day and year first above written.

                             UNITED RENTALS, INC.


                             By_____________________________
                                 Chief Financial Officer


                             UNITED RENTALS (NORTH AMERICA),
                             INC.


                             By_____________________________
                                 Chief Financial Officer


                             BANK OF AMERICA NATIONAL TRUST
                             AND SAVINGS ASSOCIATION, as U.S.
                             Agent


                             By_____________________________
                             Title__________________________


                             BANK OF AMERICA NATIONAL TRUST
                             AND SAVINGS ASSOCIATION, as a U.S.
                             Bank, as Issuing Bank and as Swing Line Bank


                             By_____________________________
                             Title__________________________


                             THE BANK OF NEW YORK, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                                      S-1
<PAGE>

                             CREDIT LYONNAIS NEW YORK BRANCH,
                              as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             DEUTSCHE BANK AG, New York Branch
                             and/or Cayman Islands Branch, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             By_____________________________
                             Title__________________________


                             ALLFIRST BANK, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             SUMMIT BANK, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             NATIONAL CITY BANK, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                                      S-2
<PAGE>

                             BANKBOSTON, N.A., as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             COMERICA BANK, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             FLEET BANK, N.A., as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             HARRIS TRUST AND SAVINGS BANK,
                              as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             THE BANK OF NOVA SCOTIA, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             UNION BANK OF CALIFORNIA, N.A., as a
                             U.S. Bank


                             By_____________________________

                                      S-3
<PAGE>

                             Title_____________________________


                             CIBC INC., as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             LASALLE BANK NATIONAL
                             ASSOCIATION, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             CITICORP DEL-LEASE, INC., as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             ERSTE BANK DER OESTERREICHISCHEN
                             SPARKASSEN AG-NEW YORK, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             THE LONG-TERM CREDIT BANK OF
                             JAPAN,  LIMITED, New York Branch, as a U.S.
                             Bank


                             By_____________________________
                             Title__________________________

                                      S-4
<PAGE>

                             CITY NATIONAL BANK, as a U.S. Bank


                             By_____________________________
                             Title__________________________


                             FUJI BANK, LIMITED, as a U.S. Bank

                             By_____________________________
                             Title__________________________


                             BANKERS TRUST COMPANY, as a U.S. Bank

                             By_____________________________
                             Title__________________________

                                      S-5
<PAGE>

                             WELLS FARGO BANK, N.A., as a U.S. Bank

                             By_____________________________
                             Title__________________________

                                      S-6