Exhibit 99.1

Rainmaker Reports First Quarter 2011 Financial Results

Campbell, Calif., May 16, 2011 – Rainmaker Systems, Inc. (NASDAQ: RMKR), a leading global provider of B2B e-commerce solutions that drive online sales and renewal for products, subscriptions and training for our clients and their channel partners, today reported financial results for its first quarter ended March 31, 2011.

Net revenue in the first quarter of 2011 was $8.8 million compared to adjusted net revenue in the preceding quarter of $8.9 million, which excludes revenue from discontinued client programs. First quarter 2011 net revenue grew 12% year-over-year compared to adjusted net revenue of $7.9 million in the first quarter of 2010, which excludes revenue from discontinued client programs and a non-recurring contract buyout. See Exhibit A for a reconciliation of GAAP net revenue to adjusted net revenue.

Recent Business Highlights

Rainmaker CEO Michael Silton commented, “We signed multiple new client wins and expansions, including launching a new B2B client on our next generation e-commerce platform, and our current sales pipeline is robust and growing and includes an expanding base of potential e-commerce clients. We have made significant progress in building a world-class sales organization to accelerate our revenue growth and capitalize on the significant opportunity we see for our B2B e-commerce solutions, which leverage the web and global sales agents to drive higher customer acquisition, renewals, subscriptions and training sales for our clients with a focus on their mid-market customers. We expect sequential growth in the second quarter with accelerating growth in the second half of this year.”

First quarter 2011 adjusted EBITDA, which excludes non-cash stock compensation expense, was negative $1.3 million, compared to negative $629,000 in the preceding quarter. See Exhibit B for a reconciliation of GAAP net income (loss) to EBITDA and adjusted EBITDA.

Gross margin in the first quarter of 2011 was 35%, compared to 37% in the preceding quarter.

Net loss for the first quarter of 2011 was $3.1 million, or a loss of $0.15 per share, compared to a net loss for the preceding quarter of $2.8 million, or a loss of $0.13 per share.

First quarter 2011 non-GAAP net loss, which excludes stock-based compensation expense of $625,000, amortization of intangible assets from acquisitions of $117,000, charges relating to facility closures of $99,000 and a $70,000 gain on fair value re-measurement, was $2.3 million, or a loss of $0.11 per share, compared to a non-GAAP net loss for the preceding quarter of $2.0 million, or a loss of $0.10 per share. See Exhibit C for a reconciliation of GAAP net income (loss) to non-GAAP net loss.

Total shares outstanding at March 31, 2011 were approximately 23.3 million common shares, which include approximately 2.2 million unvested restricted shares. In addition, Rainmaker had 704,000 unexercised options outstanding with a weighted average exercise price of approximately $2.05 per share.

Total cash and cash equivalents were $9.4 million at March 31, 2011, compared to $12.2 million at December 31, 2010. Cash used in the first quarter of 2011 included approximately $446,000 for capital equipment purchases, compared to fourth quarter 2010 purchases of $466,000. Rainmaker is carefully managing its cash balance and expects usage of cash to decline over the remainder of the year as unfavorable balance sheet changes due to timing differences of approximately $519,000 in the first quarter are not expected to recur, the Company has converted its term loan payments into interest only payments resulting in an approximately $300,000 reduction per quarter in financing cash outflows, and operating cash outflows are expected to be lower as a result of new business and steps taken to reduce non-sales spending.

Financial Guidance

Rainmaker is reiterating its fiscal year 2011 revenue guidance of approximately $40 million to $42 million, representing adjusted net revenue growth of 15% to 20% over 2010 adjusted net revenue.

Conference Call

Rainmaker Systems will host a conference call and webcast today at 1:30 p.m. Pacific Time to discuss its first quarter fiscal 2011 financial results. Those wishing to participate in the live call should dial (866) 225-8754 using the password “Rainmaker.” A replay of the call will be available for one week beginning approximately one hour after the call’s conclusion by dialing (800) 406-7325 and entering 4432459 followed by the “#” key when prompted for a code. To access the live webcast of the call, go to the Investors section of Rainmaker’s website at www.rainmakersystems.com. A webcast replay of the conference call will be available for one year on the Conference Calls/Events page of the Investors section at www.rainmakersystems.com.

Discussion of Non-GAAP Financial Measures

Rainmaker Systems’ management evaluates and makes operating decisions using various performance measures. In addition to GAAP results, Rainmaker also considers non-GAAP net loss and non-GAAP net loss per share, EBITDA and adjusted EBITDA, which excludes non-cash stock compensation expense from EBITDA. These non-GAAP measures are derived from the revenue generated by Rainmaker’s business and the costs directly related to the generation of that revenue, such as costs of services, sales and marketing expenses, technology expenses and general and administrative expenses, that management considers in evaluating the Company’s operating performance. These non-GAAP measures exclude certain revenues and expenses that management does not consider to be related to the Company’s core operating performance.

EBITDA was negative $1.9 million for the first quarter of 2011. EBITDA consists of net loss excluding interest and other expense, income taxes, depreciation & amortization and certain other non-cash items. Provision for income taxes was $69,000 for the three months ended March 31, 2011. Non-cash charges for depreciation of property and equipment were $1.0 million for the three months ended March 31, 2011. Non-cash charges for amortization of acquisition related intangibles were $117,000 for the three months ended March 31, 2011, and related to the prior acquisitions of ViewCentral, Qinteraction, Grow Commerce and Optima. A gain on fair value remeasurement was $70,000 for the three months ended March 31, 2011 and related to a reduction in the accrued liability for the potential earnout from the acquisition of Optima. Interest and other expense was $37,000 for the three months ended March 31, 2011. Adjusted EBITDA was negative $1.3 million for the three months ended March 31, 2011 and adds back to EBITDA non-cash stock based compensation expense of $625,000 incurred in the first quarter of 2011. See Exhibit B for a reconciliation of GAAP net income (loss) to EBITDA and adjusted EBITDA.

Non-GAAP net loss was $2.3 million for the first quarter of 2011 and consists of net loss excluding stock based compensation expense, amortization of purchased intangible assets, charges related to the closure of the Montreal facility and a gain on fair value remeasurement. Stock based compensation expense was $625,000 for the three months ended March 31, 2011 and represents the current quarter recognition of compensation expense related to stock options and restricted stock awards granted prior to and during the quarter. Amortization of intangible assets was $117,000 for the three months ended March 31, 2011 and related to the prior acquisitions of ViewCentral, Qinteraction, Grow Commerce and Optima. A $99,000 charge was recorded in the three months ended March 31, 2011 for our Montreal facility’s remaining lease commitment through December 31, 2011 relating to our exit from the facility. The gain on the fair value remeasurement was $70,000 for the three months ended March 31, 2011 and related to a reduction in the accrued liability for the potential earnout from the acquisition of Optima. See Exhibit C for a reconciliation of GAAP net income (loss) to non-GAAP net loss.

Non-GAAP net loss, non-GAAP net loss per share, EBITDA and adjusted EBITDA are supplemental measures of Rainmaker’s performance that are not required by, or presented in accordance with, GAAP. Moreover, they should not be considered as an alternative to any performance measure derived in accordance with GAAP, or as an alternative to cash flow from operating activities or as a measure of liquidity. Rainmaker presents these non-GAAP measures because management considers them to be important supplemental measures of Rainmaker’s operating performance and profitability trends, and because management believes they give investors useful information on period-to-period performance as evaluated by management. Rainmaker believes that the use of these non-GAAP measures provides consistency and comparability with Rainmaker’s past financial reports and also facilitates comparisons with other companies in Rainmaker’s industry, a number of which use similar non-GAAP financial measures to supplement their GAAP results. Management has used these non-GAAP measures when evaluating operating performance because management believes that the inclusion or exclusion of the items described above provides an additional measure of the Company’s core operating results and facilitates comparisons of the Company’s core operating performance against prior periods and the Company’s business model objectives. Rainmaker has chosen to provide this information to investors to enable them to perform additional analyses of past, present and future operating performance and as a supplemental means to evaluation of the Company’s ongoing core operations.

About Rainmaker

Rainmaker Systems, Inc. is a leading global provider of B2B e-commerce solutions that drive online sales and renewal for products, subscriptions and training for our clients and their channel partners. Rainmaker provides these solutions on a consistent, global basis supporting multiple payment methods, currencies and language capabilities. For more information, visit http://www.rainmakersystems.com or call 800-631-1545.

NOTE: Rainmaker Systems and the Rainmaker logo are registered with the U.S. Patent and Trademark Office. All other service marks or trademarks are the property of their respective owners.

This press release contains forward-looking statements regarding future events. These forward-looking statements are based on information available to Rainmaker as of this date and we assume no obligation to update any such forward-looking statements. These statements are not guarantees of future performance, and actual results could differ materially from current expectations. Among the important factors which could cause actual results to differ materially from those in the forward-looking statements are our client concentration, as we depend on a small number of clients for a significant percentage of our revenue, the possibility of the discontinuation and/or realignment of some client relationships, general market conditions, the current difficult macro-economic environment and its impact on our business, as our clients are reducing their overall marketing spending and our clients’ customers are reducing their purchase of services contracts, the high degree of uncertainty and our limited visibility due to economic conditions, our ability to execute our business strategy, our ability to integrate acquisitions without disruption to our business, the effectiveness of our sales team and approach, our ability to target, analyze and forecast the revenue to be derived from a client and the costs associated with providing services to that client, the date during the course of a calendar year that a new client is acquired, the length of the integration cycle for new clients and the timing of revenues and costs associated therewith, our ability to expand our channel hosted contract solution and drive adoption of this solution by resellers, potential competition in the marketplace, the ability to retain and attract employees, market acceptance of our service programs and pricing options, our ability to maintain our existing technology platform and to deploy new technology, our ability to sign new clients and control expenses, and the financial condition of our clients’ businesses, our ability to raise additional equity or debt financing, and other factors detailed in the Company’s filings with the Securities and Exchange Commission, including our filings on Forms 10-K and 10-Q.

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– Financial tables to follow –

RAINMAKER SYSTEMS, INC.

CONSOLIDATED BALANCE SHEETS

(In thousands, except share data)

(Unaudited)

RAINMAKER SYSTEMS, INC.

CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except per share amounts)

(Unaudited)

RAINMAKER SYSTEMS, INC.

CONSOLIDATED STATEMENTS OF CASH FLOWS

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RAINMAKER SYSTEMS, INC.

EXHIBIT A

RECONCILIATION OF GAAP NET REVENUE TO ADJUSTED NET REVENUE (1)

(In thousands)

(Unaudited)

RAINMAKER SYSTEMS, INC.

EXHIBIT B

RECONCILIATION OF NET INCOME (LOSS) TO EBITDA AND ADJUSTED EBITDA (1)

(In thousands)

(Unaudited)

RAINMAKER SYSTEMS, INC.

EXHIBIT C

RECONCILIATION OF GAAP NET INCOME (LOSS) TO NON-GAAP NET LOSS (1)

(In thousands, except per share)

(Unaudited)