Position limits are found at: http://www.cftc.gov/opa/backgrounder/opaspeclmts.htm#speclmts
Reporting levels are at: http://www.cftc.gov/dea/dearlevel2.htm
The S&P has a reporting level of 1,000 contracts. Those are full contracts, so it's 5,000 S&P e-minis (ES).