On October 26, 2013, about 1345 central daylight time, a Cessna 150H, N684RA, was substantially damaged during a precautionary landing and subsequent nose-over near Livingston, Alabama. The two commercial pilots on board were not injured. Visual meteorological conditions (VMC) prevailed, and no flight plan was filed for the personal flight, which originated from Cullman Regional Airport (CMD), Cullman, Alabama, about 1215. The flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.Following his purchase of the airplane, the pilot serviced the airplane with fuel at the self-service fuel pumps before departing to his home airport. He stated that after approximately 45 minutes of flight, he noticed that the alternator was "discharging," and that the fuel quantity displayed on the gauges was rapidly decreasing. The pilot then elected to perform a precautionary landing to a field. At touchdown, the nose landing gear dug into the soft soil and the airplane nosed over, which resulted in substantial damage to the engine firewall. When asked how the engine was performing, the pilot/owner said, "The engine was running fine…" and that it "did not quit." Sometime after the airplane departed CMD, a fuel cap similar to those installed on the accident airplane make and model was found at the self-service fuel pumps. The pilot recovered the airplane from the accident site, and transported it by truck to his home in Louisiana, but did not report the accident until January 16, 2014. During recovery, he noted that one fuel tank was empty, and the other contained about "1/4 tank" of fuel. He added, "So it's a good thing I landed when I did, because it wasn't the gauges, they were reading accurately" Photographs of the wreckage revealed a collapsed nose landing gear and substantial damage to the engine firewall. The wings were removed, and the fuel tanks had been removed from the wings. One tank had a fuel cap installed, while the other did not. The pilot and a mechanic he hired determined that the airplane had both a "bad fuel line" as well as an electrical problem. According to Federal Aviation Administration (FAA) and maintenance records, the airplane was manufactured in 1968. Its most recent annual inspection was completed May 18, 2013, at 7,173 total aircraft hours. The airplane was equipped with two fuel tanks, one in each wing, and each were serviced through a capped port on top of the wing. The total fuel capacity was 26 gallons, or 13 gallons per tank, of which a total of 22.5 gallons were usable. The pilot/owner held a commercial private pilot certificate with ratings for airplane single engine, multiengine, and instrument airplane. His most recent FAA third class medical certificate was issued in January, 2014. ADDITIONAL INFORMATION Both fuel caps were forwarded to the NTSB Materials Laboratory in Washington, DC for examination. While similar, the caps were not identical. Examination by a materials specialist revealed that the red paint on each cap was consistent with the paint on the other. Prior to the precautionary landing, the airplane traveled approximately 140 miles in calm winds. Interpolation of performance, fuel consumption charts, and a 100 mile-per-hour cruising speed revealed an average fuel consumption rate of 6 gallons per hour. Engine start, run-up, taxi, takeoff, and initial climb were not computed.