The pilot reported that during a 4.5-hour cross-country flight, and after making two full stop landings without refueling, the engine lost power while he was returning to his departure airport. A forced landing was made to a service road where during the landing roll, the left wing tip struck a wood post, which caused the airplane to rotate 90 degrees. The airplane sustained substantial damage to both wings. A postaccident examination revealed no usable fuel in the fuel tanks. The pilot reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation and said it was likely that he had exhausted his fuel supply.