Online staffing firm Freelancer.com announced today it acquired vWorker. Both firms rank among the six major players in online staffing, according to a report from Staffing Industry Analysts. Terms of the transaction were not announced.

Online staffing involves staffing buyers contracting with workers online for tasks that are done remotely. Workers are independent contractors or, in some cases, W-2 employees. Often the buyer and worker never meet in person.

vWorker is based in Tampa, Fla., and reports it has 2.5 million users. It was founded in 2001 by Ian Ippolito under the name “Rent a Coder,” and focused on information technology work. Staffing Industry Analysts reports vWorker had estimated revenue of approximately $50 million.

Freelancer.com is based in Australia and has estimated 2011 revenue of greater than $50 million, according to Staffing Industry Analysts.