On May 14, 1994, at 1230 central daylight time, a Cessna 150J, N51150, sustained substantial damage during a forced landing near Del Rio, Texas. The commercial pilot and a pilot rated passenger were not injured. Visual meteorological conditions prevailed for the personal cross country flight. The pilot reported in his enclosed pilot/operator report that the flight departed with full fuel from Del Rio, Texas, on May 13, 1994, and flew a 2 hour trip to Fort Stockton, Texas. The next morning a 40 minute trip was made to Alpine, Texas, where 5 gallons of fuel was added for the return flight to Del Rio, Texas. The pilot further reported that each leg of the trip was flown at 6,500 feet MSL and a 2,500 RPM setting with a calculated fuel burn of 5 gallons per hour. During the cruise descent, at approximately 3 to 5 miles from the destination airport, a total loss of engine power occurred. The pilot selected a field behind and to the right of the airplane's flight path. Due to his better view of the field, the pilot rated passenger in the right seat manipulated the controls from 600 feet above the ground during the emergency. According to the pilot/operator report, he had 1.7 hours in this make and model airplane. The airplane impacted several trees and a fence prior to coming to rest adjacent to the field. According to the enclosed mechanic statement, the total fuel recovered from the tanks was 2.5 gallons. The total time on the Hobbs meter for the trip was 4.8 hours. Manufacturer data indicates the fuel tank capacity as 26 gallons with 3.5 gallons as unusable fuel. The original departure with 26 gallons of fuel and the added five gallons of fuel gave a total of 31 gallons for the flight. Subtracting the 3.5 gallons of unusable fuel would leave 27.5 gallons usable fuel for the trip. Based on information from the pilot and the manufacturer, the Federal Aviation Administration (FAA) inspector (statement enclosed) calculated 28.8 gallons of usable fuel needed for the trip. In his pilot/operator report, the pilot-in-command stated a cruise fuel burn as 5 gph. The pilot rated passenger stated that according to their calculations refueling with 5 gallons of fuel should have given enough fuel for the return flight.