The U.S. added an estimated 55,000 nonfarm, private sector jobs in May on a seasonally adjusted basis, according to Automatic Data Processing Inc.'s (NYSE: ADP) monthly employment report released today.

In addition, the report revised its estimate of jobs gained in April to an increase of 65,000 from an increase of 32,000.

ADP reported the U.S. gained 78,000 service-sector jobs in May but lost 23,000 jobs in the goods-producing sector.

The U.S. Bureau of Labor Statistics will release employment numbers for May tomorrow. Unlike the BLS report, ADP's report does not include federal hiring in May for the 2010 Census.

The ADP report is derived from an anonymous subset of approximately 500,000 U.S. business clients.