The pilot had just purchased fuel at a self-serve gas pump prior to departure on a cross country flight. About an hour after he departed, the engine stopped producing power and he made a forced landing to a soybean field. The airplane’s nose gear collapsed, and the airplane flipped over on to its back resulting in substantial damage to the left and right wings. The pilot reported that following the accident, the left-wing fuel cap was missing and that neither fuel tank contained any fuel. While the pilot said that he replaced both fuel caps after he fueled the airplane, the left wing fuel cap was later found next to the gas pump where he pumped the fuel. A functional test of the cap revealed that it fit securely to the left-wing fuel port. As a result, it is most likely that the pilot failed to properly install the left-wing fuel cap after refueling the airplane, which resulted in loss of engine power due to fuel exhaustion in-flight.