On June 12, 1994, about 1426 central daylight time, a Cessna 182, N94752, piloted on the pleasure flight by the private pilot/registered owner's son, sustained substantial damage when it hit a pothole during a forced landing in a bean field near Millstadt, Illinois. The pilot reported serious injuries, the one passenger received minor injuries. Visual meteorological conditions prevailed for the flight, no flight plan was filed. The flight operated under 14 CFR Part 91, and originated from Valdosta, Georgia, at 0937. The intended destination was Parks Downtown Airport (CPS) at Cahokia, Illinois. The pilot stated he observed as the airplane was refueled prior to departure. He reported the fuel quantity gauges indicated full tanks. He stated the airplane was equipped with extended range fuel tanks, for a total fuel capacity of 80 gallons, with 75 gallons useable. The pilot's fuel consumption calculations indicated there was sufficient fuel for the estimated five hour flight, plus one hour reserve at normal cruise. The pilot stated almost 5 hours after the airplane departed Valdosta, "...the engine cut out....restarted and ran again for a short period, and then stopped." The airplane nosed down during the forced landing in a field approximately 8 miles southeast of the destination airport. Postaccident investigation revealed no evidence of preimpact mechanical anomaly, and no evidence of useable fuel within the fuel system. The pilot stated when he examined the airplane after the accident, "...there were fuel streaks on the right wing that had not been there before, and indicated a fuel system failure (siphoned)." The pilot's father/airplane owner stated he and his son typically did not climb up on the wing to inspect the fuel caps during the preflight inspection. The FAA Inspector stated the fuel caps did not appear loose, had good seals, and fuel cap vents installed in accordance with the applicable AD note. The FAA Inspector's statement is appended.