The pilot reported that he and his friend went to purchase an airplane from an airport in North Carolina. After an inspection and test flight of the airplane, he stated that, “we filled both tanks and called it a day.” The pilot returned the next day to pick up the airplane and said that he checked the fuel tanks and they looked full. He departed the airport enroute home and climbed to an altitude of 4,500 ft. He was aloft for 3 hours, using the right tank for 1 hour 30 minutes, followed by the left tank for 1 hour 30 minutes. He said that the engine “quit running” and he switched back to the right fuel tank. The engine started and ran for a few minutes before stopping again. The pilot elected to conduct an emergency landing on a rough logging road. After the emergency landing, the pilot checked the fuel tanks and stated that they were both empty. During a telephone interview with the pilot, he stated that his friend refueled the airplane, and he did not know how much fuel was put into the tanks. The Federal Aviation Administration inspector who responded to the scene confirmed that both fuel tanks were empty of fuel. He did not observe any breaches of the fuel tanks, nor did he find any anomalies of the fueling system. During inspection of the airplane by a mechanic, structural damage was discovered on the firewall. The engine mount was also observed buckled.