The pilot of the experimental, amateur-built airplane reported that the airplane contained about 13 gallons of fuel prior to takeoff for a 1-hour local flight. After flying for about 30 minutes, the pilot switched from the left to the right fuel tank. Shortly thereafter, the engine lost power. The pilot thought he accidently ran out of fuel; however, the header fuel tank gauge indicated a full tank. Due to the airplane’s low altitude at the time of the engine power loss, the pilot executed a forced landing to a mowed wheat field which was surrounded by a low-profile fence. During the landing, the airplane contacted the fence and nosed over. The airplane sustained substantial damage to both wings and rudder. The airplane’s fuel system consisted of a fuel tank in each wing that gravity fed to a header tank. The header tank contained two internal fuel pumps that delivered fuel to the engine driven fuel pump. The header tank was equipped with a “Motor Meter Racing Fuel Level” gauge. A postaccident examination and a functional test of the engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. A functional test of the fuel gauge determined the gauge was inoperative.