The 2,000-hour private pilot reported that his single-engine airplane lost power while at an altitude of 8,000 feet MSL during a night VFR flight. As a precaution, the pilot elected to initiate the descent to his destination airport after successfully restarting the engine. While descending to the airport, the engine lost power a second time and the pilot elected to perform a gear-up forced landing to an open field 2 nautical miles northeast of his intended destination. Additionally, the pilot noted that the right fuel gauge indicated one-fourth full and the left fuel gauge indicated an unknown low amount of fuel. The airplane sustained structural damage during the forced landing. The 3 occupants reported that they were able to egress from the airplane unassisted. Having flown this route multiple times, the pilot stated that he always landed with 45 minutes of fuel in reserve. The pilot added that the fuel gauges on his airplane were usually accurate and he was unaware of his low fuel condition until after the engine lost power the second time. The FAA investigators that responded to the accident site reported that both the left and right fuel tanks had been exhausted. Weather at the destination airport 5 minutes after the mishap was reported as calm winds, visibility 10 statute miles, with clear skies, temperature 23 degrees Celsius, dew point 18 degrees Celsius, and altimeter 30.08 inches of Mercury.