On January 3, 2003, about 0912 eastern standard time, a Cessna 150K, N6098G, registered to a private individual, experienced a partial loss of engine power and was substantially damaged during a forced landing in a field near Jessup, Georgia. Visual meteorological conditions prevailed at the time and a visual flight rules (VFR) flight plan was filed and activated for the 14 CFR Part 91 personal flight from Brunswick to Macon, Georgia. The private-rated pilot, the sole occupant, was not injured. The flight originated about 0830, from the Malcolm McKinnon Airport, Brunswick, Georgia. The pilot stated that the flight departed with full fuel tanks (26 gallons total) and approximately 40 minutes into the flight while flying at 2,400 feet mean sea level, the engine rpm decreased suddenly from 2,400 to 1,500. The engine continued to operate at 1,500 rpm and was running smoothly. Carburetor heat was applied and the throttle and mixture controls were manipulated with no response; the engine rpm remained at 1,500. He communicated with Macon Automated Flight Service Station and advised of the loss of engine power and of an impending off field landing. He maneuvered the airplane for a landing on a service road among a large area of small pines trees, and during flare to land, the left wing tip contacted a 3-inch diameter tree trunk which was not visible during the approach. The airplane cart wheeled to the left, and the nose landing gear separated after contacting soft ground. The airplane then nosed over and the pilot exited the airplane from the left door which had popped open. He later stated that he did not see any fuel leakage after exiting the airplane. He estimated the airplane remained inverted for approximately 24 hours. According to the Macon, Georgia, Automated Flight Service Station quality assurance manager, the pilot activated his VFR flight plan while airborne between 0830 and 0832, and contacted the facility again while airborne at 0910. At the second contact he advised of having a fuel problem and was losing altitude. The pilot contacted the facility again using a cellular phone at 0942 hours. NTSB review of the tape of the in-flight contact with Macon AFSS revealed the pilot did in fact advise he was having a fuel problem and was losing altitude. The FAA did not examine the airplane at the scene. According to the FAA inspector who examined the airplane following recovery, both fuel tank caps were loose when installed, and the fuel vent diaphragm of the right wing fuel cap was observed to be torn. Aft streaking of fuel from both fuel caps was noted; the fuel cap seals were poor. There was only residual fuel noted in both fuel tanks, the amount was not quantified. The gascolator bowl was found to only have 1/4 inch of fuel, while the carburetor bowl was empty. A differential compression test was performed before an attempted engine run; cylinders 1, 3, and 4, were recorded to be 76 or better when tested against 80 psi. The No. 2 cylinder differential compression check was 12 psi. The engine run was performed on airframe with the accident propeller installed; the impact damaged propeller was straightened for the attempted engine run. The engine was started and operated to approximately 2,000 rpm; no discrepancies were noted during the engine run. Magneto checks performed at idle indicate each dropped 75 rpm, and the oil pressure was 45 psi during the run. Safety concerns prevented operation at a higher rpm. Examination of photographs taken of the airplane at the scene revealed the leading edges of both wings was at a lower elevation than the trailing edges.