The 72-hour private pilot reported that approximately 2-hours and 10-minutes into his 425-nautical mile flight, while in cruise flight at 5,500 feet MSL, his single-engine airplane experienced a complete loss of engine power. Several attempts to re-start the engine were unsuccessful and the pilot elected to execute a forced landing to a grass field. During the emergency descent, the pilot noted that the left and right fuel gauges indicated approximately one-fourth a tank of fuel per side. During the landing roll the nose landing gear sunk into the soft ground and the airplane nosed-over coming to rest in an inverted position. The pilot was able to exit the airplane unassisted. A Federal Aviation Administration (FAA) inspector responded to the accident site and examined the airplane. The inspector reported that both fuel tanks were found empty and that they did not appear to be compromised. In addition, the inspector reported that he did not observe fuel stains suggesting the fuel had leaked out. The inspector further reported that the right wing had sustained structural damage. The pilot reported that he performed a pre-flight inspection of the airplane and visually verified that both fuel tanks were full prior to departure. Fueling records at the departure airport established that the airplane was last fueled two days earlier, with the addition of 30.6 gallons of fuel. The homebuilt airplane had a total fuel capacity of 38-gallons, which provides for a cross-country range of approximately 3 hours and 45 minutes. The pilot had planned for a 2 hour and 29 minute flight. The airplane was powered by a Lycoming O-360-A1D engine. According to the operator's manual for the engine, the normal fuel consumption rate for that engine is 10.5 gallons per hour at 2,450 rpm (75 percent rated power).