The airplane was refueled the day before the flight and the fuel tanks were checked again during the preflight inspection. The flight departed Somerville, New Jersey, with 90 gallons of fuel on board. The pilot computed 16 gallons of fuel usage per hour and about 5 hours of fuel endurance. About 2 hours and 45 minutes into the flight, the pilot switched fuel tanks and immediately noticed a faster than normal drop on the fuel quantity gauge. The pilot informed ATC at Myrtle Beach of his fuel status, and elected to land at Myrtle Beach for fuel. Both engines quit and the pilot made a forced landing in a field about 3 miles from the airport. There was no fuel found in the fuel tanks when the airplane was examined at the accident site and there were no obvious signs of fuel leakage from the fuel tanks at the accident site or fuel stains on the airplane. However, while conducting airframe repairs, the repair facility discovered a substantial fuel leak from the left main fuel cell. Cracks, typical of aging, were discovered in the inboard corners of the fuel bladder when it was removed from the airplane. The bladder was manufactured by Piper in 1980.