GUARANTY SUPPLEMENT

Exhibit 10.6

GUARANTY SUPPLEMENT

April 30, 2012

To: Bank of America, N.A., as Agent

Ladies and Gentlemen:

Reference is made to (i) the Amended and Restated Credit Agreement, dated as of October 14, 2011 (as amended, restated, extended, supplemented or otherwise modified in writing from time to time, the “Credit Agreement”), among United Rentals, Inc., a Delaware corporation (“Holdings”), United Rentals (North America), Inc., a Delaware corporation (the “Company”), the other U.S. Subsidiary Borrowers named therein (together with the Company, the “U.S. Borrowers”), United Rentals of Canada, Inc., a corporation amalgamated under the laws of the Province of Ontario (the “Canadian Borrower”), United Rentals Financing Limited Partnership (the “Specified Loan Borrower”), the Lenders from time to time party thereto, and Bank of America, N.A., as Agent and (ii) the U.S. Guarantee Agreement referred to in the Credit Agreement (such U.S. Guarantee Agreement, as in effect on the date hereof and as it may hereafter be amended, supplemented or otherwise modified from time to time, together with this Guaranty Supplement, being the “Guaranty”). The capitalized terms defined in the Guaranty or in the Credit Agreement and not otherwise defined herein are used herein as therein defined.

Section 1. Guaranty; Limitation of Liability. (a) Each of the undersigned hereby absolutely, unconditionally and irrevocably guarantees the punctual payment when due, whether at scheduled maturity or on any earlier date of a required prepayment by reason of acceleration, demand or otherwise, of all Obligations of each other Obligor, whether now or hereafter existing (including, without limitation, any extensions, modifications, substitutions, amendments or renewals of any or all of the foregoing Obligations), whether direct or indirect, absolute or contingent, and whether for principal, interest, premium, fees, indemnities, contract causes of action, costs, expenses or otherwise (such Obligations being the “Guaranteed Obligations”), and agrees to pay any and all expenses (including, without limitation, Attorney Costs) incurred by the Agent or any other Secured Party (to the extent provided for in the Credit Agreement) in enforcing any rights under this Guaranty Supplement, the Guaranty or any other Loan Document. Without limiting the generality of the foregoing, each of the undersigned’s liability shall extend to all amounts that constitute part of the Guaranteed Obligations and would be owed by any other Obligor to any Secured Party but for the fact that they are unenforceable or not allowable due to the existence of a bankruptcy, reorganization or similar proceeding involving such other Obligor.

(b) Each of the undersigned, and by its acceptance of this Guaranty Supplement, the Agent and each other Secured Party, hereby confirms that it is the intention of all such Persons that this Guaranty Supplement, the Guaranty and the Obligations of each of the undersigned hereunder and thereunder not constitute a fraudulent transfer or conveyance for purposes of Bankruptcy Law, the Uniform Fraudulent Conveyance Act, the Uniform Fraudulent Transfer Act or any similar foreign, federal or state law to the extent applicable to this Guaranty Supplement, the Guaranty and the Obligations of each of the undersigned hereunder and

thereunder. To effectuate the foregoing intention, the Agent, the other Secured Parties and each of the undersigned hereby irrevocably agree that the Obligations of each of the undersigned under this Guaranty Supplement and the Guaranty at any time shall be limited to the maximum amount as will result in the Obligations of such undersigned under this Guaranty Supplement and the Guaranty not constituting a fraudulent transfer or conveyance.

(c) Each of the undersigned hereby unconditionally and irrevocably agrees that in the event any payment shall be required to be made to any Secured Party under this Guaranty Supplement, the Guaranty, the Canadian Guarantee Agreement or any other guaranty, such undersigned will contribute, to the maximum extent permitted by applicable law, such amounts to each other Guarantor (as such term is defined in the Credit Agreement) so as to maximize the aggregate amount paid to the Secured Parties in respect of the Guaranteed Obligations.

Section 2. Obligations Under the Guaranty. Each of the undersigned hereby agrees, as of the date first above written, to be bound as a Guarantor by all of the terms and conditions of the Guaranty to the same extent as each of the other Guarantors thereunder. Each of the undersigned further agrees, as of the date first above written, that each reference in the Guaranty to an “Additional Guarantor” or a “Guarantor” shall also mean and be a reference to such undersigned.

Section 3. Representations and Warranties. Each of the undersigned hereby makes each representation and warranty set forth in Section 6 of the Guaranty to the same extent as each other Guarantor.

Section 4. Delivery by Telecopier. Delivery of an executed counterpart of a signature page to this Guaranty Supplement by telecopier or other electronic communication shall be effective as delivery of an original executed counterpart of this Guaranty Supplement.

Section 5. Governing Law; Jurisdiction; Waiver of Jury Trial, Etc. (A) THIS GUARANTY SUPPLEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK. ANY LEGAL ACTION OR PROCEEDING WITH RESPECT TO THIS GUARANTY SUPPLEMENT MAY BE BROUGHT IN THE COURTS OF THE STATE OF NEW YORK OR OF THE UNITED STATES OF AMERICA LOCATED IN NEW YORK COUNTY, AND BY EXECUTION AND DELIVERY OF THIS GUARANTY SUPPLEMENT, EACH OF THE UNDERSIGNED CONSENTS, FOR ITSELF AND IN RESPECT OF ITS PROPERTY, TO THE NONEXCLUSIVE JURISDICTION OF THOSE COURTS.

(B) EACH OF THE UNDERSIGNED HEREBY IRREVOCABLY AND UNCONDITIONALLY SUBMITS, FOR ITSELF AND ITS PROPERTY, TO THE NONEXCLUSIVE JURISDICTION OF ANY NEW YORK STATE COURT OR ANY FEDERAL COURT OF THE UNITED STATES OF AMERICA SITTING IN NEW YORK CITY, AND ANY APPELLATE COURT FROM ANY THEREOF, IN ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS GUARANTY SUPPLEMENT, THE GUARANTY OR ANY OF THE OTHER LOAN DOCUMENTS TO WHICH IT IS OR IS TO BE A PARTY, OR FOR RECOGNITION OR ENFORCEMENT OF ANY JUDGMENT, AND EACH OF THE UNDERSIGNED HEREBY IRREVOCABLY AND

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UNCONDITIONALLY AGREES THAT ALL CLAIMS IN RESPECT OF ANY SUCH ACTION OR PROCEEDING MAY BE HEARD AND DETERMINED IN ANY SUCH NEW YORK STATE COURT OR, TO THE EXTENT PERMITTED BY LAW, IN SUCH FEDERAL COURT. EACH OF THE UNDERSIGNED AGREES THAT A FINAL JUDGMENT IN ANY SUCH ACTION OR PROCEEDING SHALL BE CONCLUSIVE AND MAY BE ENFORCED IN OTHER JURISDICTIONS BY SUIT ON THE JUDGMENT OR IN ANY OTHER MANNER PROVIDED BY LAW. NOTHING IN THIS GUARANTY SUPPLEMENT OR THE GUARANTY OR ANY OTHER LOAN DOCUMENT SHALL AFFECT ANY RIGHT THAT ANY PARTY MAY OTHERWISE HAVE TO BRING ANY ACTION OR PROCEEDING RELATING TO THIS GUARANTY SUPPLEMENT, THE GUARANTY OR ANY OF THE OTHER LOAN DOCUMENTS TO WHICH IT IS OR IS TO BE A PARTY IN THE COURTS OF ANY OTHER JURISDICTION.

(C) EACH OF THE UNDERSIGNED IRREVOCABLY AND UNCONDITIONALLY WAIVES, TO THE FULLEST EXTENT IT MAY LEGALLY AND EFFECTIVELY DO SO, ANY OBJECTION THAT IT MAY NOW OR HEREAFTER HAVE TO THE LAYING OF VENUE OF ANY SUIT, ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS GUARANTY SUPPLEMENT, THE GUARANTY OR ANY OF THE OTHER LOAN DOCUMENTS TO WHICH IT IS OR IS TO BE A PARTY IN ANY NEW YORK STATE OR FEDERAL COURT. EACH OF THE UNDERSIGNED HEREBY IRREVOCABLY WAIVES, TO THE FULLEST EXTENT PERMITTED BY LAW, THE DEFENSE OF AN INCONVENIENT FORUM TO THE MAINTENANCE OF SUCH SUIT, ACTION OR PROCEEDING IN ANY SUCH COURT. EACH OF THE UNDERSIGNED ACKNOWLEDGES THAT ANY APPEALS FROM THE COURTS DESCRIBED IN THE IMMEDIATELY PRECEDING SENTENCE MAY HAVE TO BE HEARD BY A COURT LOCATED OUTSIDE THOSE JURISDICTIONS.

(D) EACH OF THE UNDERSIGNED HEREBY IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN ANY ACTION, PROCEEDING OR COUNTERCLAIM (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR RELATING TO ANY OF THE LOAN DOCUMENTS, THE TRANSACTIONS CONTEMPLATED HEREBY AND THEREBY OR THE ACTIONS OF ANY SECURED PARTY IN THE NEGOTIATION, ADMINISTRATION, PERFORMANCE OR ENFORCEMENT THEREOF. EACH OF THE UNDERSIGNED AGREES THAT ANY SUCH CLAIM OR CAUSE OF ACTION SHALL BE TRIED BY A COURT TRIAL WITHOUT A JURY. WITHOUT LIMITING THE FOREGOING, EACH OF THE UNDERSIGNED AGREES THAT THEIR RESPECTIVE RIGHT TO A TRIAL BY JURY IS WAIVED BY OPERATION OF THIS SECTION AS TO ANY ACTION, COUNTERCLAIM OR OTHER PROCEEDING WHICH SEEKS, IN WHOLE OR IN PART, TO CHALLENGE THE VALIDITY OR ENFORCEABILITY OF THIS GUARANTY SUPPLEMENT OR THE OTHER LOAN DOCUMENTS OR ANY PROVISION HEREOF OR THEREOF.

Section 6. Removal of Immaterial Subsidiary Designation. As of the date hereof, Holdings has removed the designation of each of the undersigned as Immaterial Subsidiaries under the Credit Agreement. Accordingly, in connection therewith and concurrently with the effectiveness of this Guaranty Supplement, as of the date hereof, the undersigned acknowledge that Section 16 of the Guaranty shall be of no further force and effect.

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[Signature Page to Guaranty Supplement]