The U.S. private sector added 162,000 jobs in September, beating analyst forecasts of a modest increase of roughly 140,000 positions, according to data from HR firm Automatic Data Processing (ADP).

Approximately 144,000 jobs were created in just the services sector, while the goods-producing sector increased payrolls by 18,000 positions.

ADP's National Employment Report also revised job gains for July and August by reducing July's earlier estimate by 17,000 positions to 156,000 new paid positions. August jobs also were revised down to 189,000 new payroll adds.

Smaller firms remained the top job creators with the development of 81,000 positions in September.

Medium-sized and large-scale businesses launched 64,000 and 17,000 jobs, respectively.

Analysts with Capital Economics pointed out that ADP's numbers are highly optimistic when compared to estimates for Friday's job report from the government.

"Even allowing for a small decline in public sector employment, that suggests our forecast that the official non-farm payroll figures will show a 100,000 gain for September could be a little pessimistic," the research firm wrote. "Nevertheless, given that the ADP survey has proved to be overly optimistic in the past four or five months, we are happy to stick with our existing call."