Allegis Group again this year ranks as the largest U.S. staffing firm based on 2010 U.S. staffing revenue of $5.77 billion, according to Staffing Industry Analysts’ 2011 list of largest U.S. staffing firms.

Adecco SA ranked as the second-largest with $4.10 billion in U.S. staffing revenue.

Rounding out the top five were ManpowerGroup Inc. (NYSE: MAN) with $3.95 billion in 2010 U.S. staffing revenue, Kelly Services Inc. (NASD: KELYA) with $3.12 billion and Robert Half International Inc. (NYSE: RHI) with $2.02 billion.

Overall, 98 firms reported at least $100 million in U.S. staffing revenue in 2010.

Corporate members of Staffing Industry Analysts can download the full list by clicking here.