EMPLOYMENT AGREEMENT

Exhibit 10.53

E MPLOYMENT A GREEMENT

T HIS A GREEMENT is entered into as of July 21, 2008, by and between A HMED  R UBAIE (the “Employee”) and A RIBA , I NC . , a Delaware corporation (the “Company”).

(a) Position . The Employee’s employment hereunder (the “Employment”) shall commence on the date of this Agreement. Effective August 10, 2008, the Employee shall be employed in the position of Executive Vice President and Chief Financial Officer. The Employee shall report to the Chief Executive Officer of the Company. The Employee shall have such duties and responsibilities as the Company may reasonably assign to him that are commensurate with his title and position with the Company. The Employee’s principal place of Employment shall be determined by the Company’s Chief Executive Officer.

(b) Obligations to the Company . During his Employment, the Employee shall devote his full business efforts and time to the Company. During his Employment, without the prior written approval of the Company, the Employee shall not render services in any capacity to any other person or entity and shall not act as a sole proprietor or partner of any other person or entity or as a shareholder owning more than five percent of the stock of any other corporation. The Employee shall comply with the Company’s policies and rules, as they may be in effect from time to time during his Employment. Notwithstanding the foregoing, nothing herein shall preclude the Employee from (i) serving on the boards of directors of a reasonable number of trade associations and/or charitable organizations, (ii) engaging in charitable activities and community affairs and (iii) managing his personal investments and affairs, provided that such activities do not materially interfere with the proper performance of his duties and responsibilities as set forth in Subsection (a) above.

(a) Salary . The Company shall pay the Employee as compensation for his services a base salary at a gross annual rate of not less than $400,000. Such salary shall be payable in accordance with the Company’s standard payroll procedures. (The annual compensation specified in this Subsection (a), together with any increases in such compensation that the Company may grant from time to time, is referred to in this Agreement as the “Base Salary.”)

(b) Signing Bonuses . Within 30 days after the Employee’s first day of Employment, the Company shall pay him $100,000 in a lump sum in cash. Within six months after the Employee’s first day of Employment (on a date determined by the Company at its sole discretion), the Company shall pay him an additional $100,000 in a lump sum in cash. The Employee shall immediately repay all amounts that he received under this Subsection (b) if he resigns his position with the Company within six months after his first day of Employment.

(c) Incentive Bonuses . Commencing with fiscal year 2009, the Employee shall be eligible to be considered for an annual incentive bonus with a target amount of not less than $200,000. The bonus shall be paid in accordance with the Company’s generally applicable bonus payment procedures for similarly situated employees. The bonus shall be awarded based on the criteria established by the Company and communicated to the Employee during the first quarter of the applicable fiscal year. Except as otherwise provided in the Agreement, the Employee shall not be entitled to an incentive bonus if he is not employed by the Company on the date when such bonus is payable in accordance with the Company’s generally applicable bonus payment procedures for similarly situated employees.

Solely with respect to fiscal year 2009, the Employee’s incentive bonus shall not be less than $150,000, of which $50,000 shall be payable in November 2008 and $100,000 shall be payable in June 2009 (collectively, the “Advance Payments”). The Employee shall not be entitled to an Advance Payment if he is not employed by the Company on the date when such Advance Payment is due. The amount of the Advance Payments shall be subtracted from the final incentive bonus earned by the Employee for Fiscal Year 2009.

(d) Initial Equity Award . Subject to the approval of the Compensation Committee of the Company’s Board of Directors, the Employee shall receive restricted stock units (the “RSUs”) representing shares of the Company’s Common Stock (the “Stock”) with a market value equal to $1,400,000, rounded off to the nearest whole share. For this purpose, the market value per share of Stock shall be deemed to be equal to the average of the closing prices on the 30 consecutive trading days immediately preceding the date of grant, as reported by The Wall Street Journal . The RSUs shall be subject to the terms and conditions applicable to stock units granted under the Company’s 1999 Equity Incentive Plan (the “Plan”), as described in the Plan and in the applicable Stock Unit Agreement. The Employee shall vest in one-third of the RSUs after 12 months from the vesting commencement date provided his service is continuous from his first date of employment, an additional one-third of the RSUs after 24 months from the vesting commencement date provided his service is continuous from his first date of employment, and the remaining one-third of the RSUs after 36 months from the vesting commencement date provided his service is continuous from his first date of employment, as described in the applicable Stock Unit Agreement.

During his Employment, the Employee shall be eligible for paid vacations in accordance with the Company’s vacation policy for similarly situated employees, as it may be amended from time to time. During his Employment, the Employee shall be eligible to participate in the retirement, medical, dental, vision, life insurance, disability, tuition assistance and other benefit and fringe benefit plans (collectively, the “Employee Benefit Plans”) maintained by the Company for similarly situated employees, subject in each case to the generally applicable terms and conditions of the plan in question and to the determinations of any person or committee administering such Employee Benefit Plan.

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(a) Business Expenses . During his Employment, the Employee shall be authorized to incur necessary and reasonable travel, entertainment and other business expenses in connection with his duties hereunder. The Company shall reimburse the Employee for such expenses upon presentation of an itemized account and appropriate supporting documentation, all in accordance with the Company’s generally applicable policies for similarly situated employees.

(b) Relocation Expenses . The Company shall reimburse the Employee for the reasonable expenses of relocating himself, his family and his household to his principal place of Employment, as determined by the Company’s Chief Executive Officer. Eligibility for reimbursement shall be determined in accordance with the Company’s relocation policy for similarly situated employees.

(a) Termination of Employment . The Company may terminate the Employee’s Employment at any time and for any reason (or no reason), and with or without cause, by giving the Employee 30 days’ advance notice in writing. The Employee may terminate his Employment at any time and for any reason (or no reason) by giving the Company 30 days’ advance notice in writing. The Employee’s Employment shall terminate automatically in the event of his death. The termination of the Employee’s Employment shall not limit or otherwise affect his obligations under Section 8.

(b) Employment at Will . The Employee’s Employment with the Company shall be “at will.” Any contrary representations that may have been made to the Employee shall be superseded by this Agreement. This Agreement shall constitute the full and complete agreement between the Employee and the Company on the “at will” nature of the Employee’s Employment, which may only be changed in an express written agreement signed by the Employee and a duly authorized officer of the Company.

(c) Rights upon Termination . Except as expressly provided in Sections 6 and 7, upon the termination of the Employee’s Employment, the Employee shall only be entitled to the compensation, benefits and expense reimbursements that the Employee has earned under this Agreement before the effective date of the termination. The payments under this Agreement shall fully discharge all responsibilities of the Company to the Employee.

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(ii) A Separation occurs because the Company terminates the Employee’s Employment for a reason other than Cause or Permanent Disability; ¹ and

(iii) Either (A) the Employee and the Company have executed a reciprocal general release (in the form attached hereto as Exhibit A ) of all known and unknown claims that they may then have against each other and have agreed not to prosecute any legal action or other proceeding based on such claims or (B) the Company (at its sole discretion) has determined within 30 days after the Separation to waive the requirement of a reciprocal general release. Absent a waiver by the Company, the Company shall complete the form of release and deliver it to the Employee within 30 days after the Separation. The Employee shall execute and return the release within the period set forth in such form.

The foregoing notwithstanding, the Employee and the Company shall not be required to release any claims that they may have against each other arising under (i) any indemnification agreement between the Employee and the Company or (ii) any rights to indemnification, advancement of expenses or repayment arising under the Company’s Amended and Restated Certificate of Incorporation or the Company’s Amended and Restated Bylaws, in each case as currently in effect or as subsequently amended.

(b) Severance Pay . If this Section 6 applies, then the Employee shall be entitled to receive severance payments from the Company for a period of 12 months following the Separation (the “Continuation Period”). Such severance payments shall be made in accordance with the Company’s standard payroll procedures and shall commence within 30 days after the Employee returns the release described in Subsection (a)(iii)(A) above or the Company makes the determination described in Subsection (a)(iii)(B) above, as applicable. The annual rate of such severance payments shall be equal to the sum of:

(i) The Employee’s Base Salary at the annual rate in effect when the Separation occurs; plus

(ii) The Employee’s annual target bonus for the fiscal year in which the Separation occurs.

In addition to any other remedies that may be available to the Company, severance payments shall cease immediately if the Employee fails to comply with the covenants set forth in Section 8.

(c) Acceleration of Vesting . If this Section 6 applies, then:

(i) The vested portion of all restricted shares of Stock held by the Employee when the Separation occurs shall at all times thereafter be determined by adding 12 months to his actual period of Employment with the Company.

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(ii) During the Continuation Period, the Employee shall continue to vest in the Equity held by him when the Separation occurs (other than restricted shares of Stock), subject to his compliance with the covenants set forth in Section 8 below. The monthly rate of vesting during the Continuation Period shall be the same as prior to the Separation.

(d) Extension of Option Exercise Period . If this Section 6 applies, then all options and other rights to purchase shares of Stock, and all stock appreciation rights measured by the value of Stock, that are held by the Employee when the Separation occurs shall remain exercisable until the earlier of:

(i) The later of (A) the date 12 months after the Separation or (B) with respect to any increment of options or rights that becomes exercisable later than nine months after the Separation, the date three months after such increment becomes exercisable; or

(ii) The date the options or rights would have expired if the Separation had not occurred.

(e) COBRA Premiums . If this Section 6 applies, and if the Employee elects to continue health insurance coverage under COBRA for himself and, if applicable, his dependents following the Separation, then the Company shall pay the employer portion of the monthly premium under COBRA for the Employee and, if applicable, such dependents until the earliest of:

(i) The end of the Continuation Period;

(ii) The expiration of the Employee’s continuation coverage under COBRA; or

(iii) The date when the Employee receives equivalent health insurance coverage in connection with new employment.

(i) The Company terminates the Employee’s Employment with the Company for a reason other than Cause or Permanent Disability within 12 months after a Change in Control; or

(ii) The Employee resigns for Good Reason within 12 months after a Change in Control.

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(b) Severance Payment . If this Section 7 applies, then the Employee shall be entitled to receive a severance payment from the Company. The amount of such payment shall be equal to 200% of the sum of:

(i) The Employee’s Base Salary at the annual rate in effect when the Separation occurs or at the annual rate in effect when the Change in Control occurs, whichever is greater; plus

(ii) The Employee’s annual target bonus for the fiscal year in which the Separation occurs.

Such payment shall be made in a lump sum in cash on the date a Separation occurs under Subsection (a)(i) above or not later than the date three business days after a Separation occurs under Subsection (a)(ii) above.

(c) Acceleration of Vesting . If this Section 7 applies, then all of the Equity held by the Employee when the Separation occurs shall become fully and unconditionally vested, fully exercisable and fully transferable (except for transfer restrictions imposed by law).

(d) Extension of Option Exercise Period . If this Section 7 applies, then all options and other rights to purchase shares of Stock, and all stock appreciation rights measured by the value of Stock, that are held by the Employee when the Separation occurs shall remain exercisable until the earlier of:

(i) The date 24 months after the Separation; or

(ii) The date such options or rights would have expired if the Separation had not occurred.

(e) COBRA Premiums . If this Section 7 applies, and if the Employee elects to continue health insurance coverage under the Consolidated Omnibus Budget Reconciliation Act (“COBRA”) for himself and, if applicable, his dependents following the Separation, then the Company shall pay the employer portion of the monthly premium under COBRA for the Employee and, if applicable, such dependents until the earliest of:

(i) The date 24 months after the Separation;

(ii) The expiration of the Employee’s continuation coverage under COBRA; or

(iii) The date when the Employee receives equivalent health insurance coverage in connection with new employment.

(a) Non-Solicitation . During his Employment and, if Section 6 applies, during the Continuation Period, the Employee shall not directly or indirectly, personally or

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through others, solicit or attempt to solicit the employment of any employee of the Company or any of the Company’s affiliates, whether on the Employee’s own behalf or on behalf of any other person or entity. The term “employment” for purposes of this Subsection (a) means to enter into an arrangement for services as a full-time or part-time employee, independent contractor, agent or otherwise. The Employee and the Company agree that this provision is reasonably enforced as to any geographic area in which the Company conducts its business.

(b) Non-Competition . The Employee agrees that, during his Employment and during the Continuation Period (if any), he shall not:

(i) Directly or indirectly, individually or in conjunction with others, engage in activities that compete with the Company or work for any entity that is part of the Company’s Market;

(ii) Solicit, serve, contract with or otherwise engage any existing or prospective customer, client or account of the Company on behalf of any entity that is part of the Company’s Market; or

(iii) Cause or attempt to cause any existing or prospective customer, client or account of the Company to divert from, terminate, limit or in any manner modify, or fail to enter into, any actual or potential business relationship with the Company. The Employee and the Company agree that this provision is reasonably enforced with reference to any geographic area in which the Company maintains any such relationship.

For purposes of this Subsection (b), the Company’s “Market” shall mean (i) all companies that derive their revenue primarily from e-procurement and/or spend management software or service sales or sales of software or services aiding companies in sourcing and/or spend management activities and (ii) those companies set forth on Exhibit B attached hereto. The Employee and the Company agree that the Company’s Market is global in scope.

(c) Cooperation and Non-Disparagement . The Employee agrees that, during the Continuation Period, he shall cooperate with and assist the Company in every reasonable respect in facilitating the transition of his duties to his successor; provided that the Employee shall not be required to devote more than 20 hours per month to providing such assistance and cooperation. The Employee further agrees that, during the Continuation Period, he shall not in any way or by any means disparage the Company, the members of the Board or the Company’s officers and employees.

(d) Disclosure . The Employee agrees that, during the Continuation Period, he shall inform any new employer or other person or entity with whom the Employee enters into a business relationship, before accepting employment or entering into a business relationship, of the existence of this Section 8.

(e) Construction . If any provision set forth in this Section 8 is not enforceable under the laws of the state in which the Employee is employed following his

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Separation, nothing in this Agreement shall prohibit the Employee from engaging in such lawful conduct; provided, however, that if the Employee elects to do so, his rights to any of the benefits set forth in Section 6 shall terminate immediately.

(a) Parachute Gross-Up Payment . If it is determined that any payment or distribution of any type to the Employee or for his benefit by the Company, any of its affiliates, any person who acquires ownership or effective control of the Company or ownership of a substantial portion of the Company’s assets (within the meaning of section 280G of the Internal Revenue Code of 1986, as amended (the “Code”), and the regulations thereunder) or any affiliate of such person, whether paid, payable, distributed or distributable pursuant to the terms of this Agreement or otherwise (the “Total Payments”), would be subject to the excise tax imposed by section