On May 8, 1998, at 1936 eastern daylight time, a Cessna 177B, N904DS, was substantially damaged during a forced landing in Prattsville, Ohio. The certificated commercial pilot and private pilot/owner were not injured. Visual meteorological conditions prevailed for the personal flight that originated at Evansville, Indiana (EVV), at 1720, destined for Parkersburg, West Virginia (PKB). An Instrument Flight Rules (IFR) flight plan was filed for the flight conducted under 14 CFR Part 91. In a telephone interview, the commercial rated pilot stated the purpose of the flight was to pick up the owner's children at PKB and return to EVV. After the airplane was towed from it's hangar, he washed the airplane, performed the pre-flight inspection, and filed the flight plan in preparation for the flight. The pilot stated he was assisted by an airport line attendant during the airplane wash and pre-flight. He said he performed the pre-flight by the checklist. The pilot stated he drained the fuel sumps and the gascolator, but did not visually check the fuel quantity in the tanks. He checked the security and alignment of the fuel caps after the line attendant checked the fuel tanks. The pilot said the co-pilot arrived while the line attendant checked the right fuel tank. According to the pilot, Air Traffic Control (ATC) assigned N904DS an altitude of 4000 feet, then 9,000 feet, after takeoff from EVV. Before the airplane climbed from 4,000 feet, the pilot noted the right fuel quantity indicator "...was all the way on 'E', the left read three-quarters." After discussion with the owner, it was decided the gauge was in error and the flight was continued. The pilot selected the right tank position on the fuel selector and flew for 50 minutes. He said this satisfied his suspicion that the right fuel gauge was inaccurate. The pilot said he then flew from the left tank to balance the fuel load and ultimately switched the selector to "Both". In cruise flight at 9,000 feet, after approximately 2 hours of flight time, the engine stopped producing power. The pilot requested and was given radar vectors to Ohio University Airport (UNI). In a telephone interview, the aircraft owner stated that with the aid of a hand-held GPS, he computed airspeed, distance, and altitude required to reach UNI. At 10 miles and approximately 6,000 feet, he determined the airport could not be reached and both pilots decided on an off-airport forced landing site. During the subsequent forced landing to sloped terrain, the airplane nosed over and came to rest inverted. Examination of the wreckage by a Federal Aviation Administration (FAA) Aviation Safety Inspector revealed no evidence of fuel at the scene. The airplane was recovered to Mt. Vernon, Ohio. On May 14, 1998, an FAA Airworthiness Inspector started and ran the airplane's engine on the airframe. The airplane had been hangared and serviced by the Fixed Base Operator (FBO) at Evansville. According to the airplane owner, the pilot, and the manager of the FBO, standard procedure was to park N904DS in front of the FBO after the last flight of the day. The airplane was then "topped off with fuel" and hangared by a line attendant. A review of aircraft records and fuel receipts revealed that, prior to the accident flight, the airplane flew 2.6 hours from Mansfield, Ohio, to Evansville, Indiana, on April, 22, 1998. A review of fuel records at the Evansville FBO revealed the last fuel service for N904DS was billed April 19, 1998. After reviewing his records, the pilot/owner stated: "I topped it off in Mansfield and I should have flown 2.6 hours back [to EVV]. Then we flew 2.1 hours and, 'Guess what?', we're at fuel endurance."