Not a measureable amount or enouhg to warrant adding any. You actually can get slightly better mileage and power if the oil level is a little lower. Less windage in the oil pan from the crank moving through it.

Are you sure your checking the oil after the engine has cooled off for at least 30 minutes? Otherwise there will still be some oil in the top end of the engine that hasn't settled back into the oil pan... which would make it read low.