The largest staffing firms have captured a bigger piece of the U.S. staffing market over the years, according to an analysis of data in lists of largest staffing firms produced by Staffing Industry Analysts.

Market share of the 15 largest staffing firms increased by an average of 2.3 percent points per year over based on revenue growth from 2007 and 2011. The five largest staffing firms alone increased their market share by an average of 1.3 percentage points a year during the same period.

U.S. market share of the 15 largest staffing firms based on 2011 revenue was 44 percent, up from 35 percent in 2007.

Among the five largest staffing firms, their market share was 25 percent in 2011, up from 20 percent in 2007.

It’s notable the market share of the largest staffing firms in the U.S. remained flat in 2008 but significantly increased in 2009.

“This might be the result you’d expect” said Theo Vadpey, author of the report. “In a recession, some firms fail, and in turn, the firms that survive receive a larger share of the market.”

The analysis also looked at rankings of largest U.S. staffing firms between 2011 and 2007. Trends found included: Allegis Group and Adecco maintained their No. 1 and No. 2 positions all five years. In addition, Insight Global moved up to No. 20 on the list of largest staffing firms in 2011 from No. 88 in 2007. Artech Information Systems rose to No. 36 from No. 103. Ambrose, Belcan and System One also greatly improved their rankings.

More information on reports by Staffing Industry Analysts can be found at www.staffingindustry.com. Corporate members of Staffing Industry Analysts can access the full version of this report, “Trends in U.S. staffing market concentration and staffing firm rankings, 2007-2011,” by clicking here.