Professional employer organization Oasis Outsourcing Holdings Inc. said it acquired Professional Employer Plans Inc., Advantage Employer Solutions Inc., and related companies. Terms of the deal were not announced. The Tampa FL-based companies provide PEO services.

The acquired companies' office in Tampa will remain in operation. The companies' president Steve Harper, and executive VP, Robert "Bo" Liess, will continue with Oasis.

"We are proud of our organic growth, which has significantly expanded our client base over the past several years," said Oasis President and CEO Mark Perlberg.

Staffing Industry Analysts ranked privately held West Palm Beach FL-based Oasis as the sixth-largest PEO in the United States based on 2005 revenue.