The pilot took off on a 2-hour flight with about 6 hours of fuel on board. On several occasions during the flight, he repositioned the fuel selector handle. He stated that when he made a very shallow turn to the right, near his destination, the engine suddenly lost power. He attempted to restart the engine by switching the fuel selector to various positions, but power was not restored. The pilot attempted to glide to the nearest airport, but had insufficient altitude. Subsequently, he landed the aircraft in a field with the gear retracted. An exam of the aircraft revealed no preimpact part failure or malfunction that would have prevented normal operation of the engine. Approximately 37 gallons of fuel was found in the four fuel tanks. The left main fuel tank was found to be empty, but fuel was found in the other tanks. One tank was virtually full; one was about half full; the other was about 10% full.