On September 30, 1999, at 1520 central daylight time, a Piper PA- 31, Canadian registration CGHOL, made an off airport forced landing in a plowed corn field in Greenfield, Indiana. The landing followed a loss of power on both engines shortly after takeoff from the Mt. Comfort Airport, Indianapolis, Indiana. The pilot, co-pilot, and five passengers were not injured. The airplane was substantially damaged. The 14 CFR Part 135 non-scheduled, international, passenger flight was operating on an IFR flight plan in visual meteorological conditions. The flight departed the Mt. Comfort Airport shortly before the accident with a destination of Waterloo, Ontario, Canada. The captain stated that the first officer was flying the airplane when the accident occurred. He stated that he performed the airplane preflight prior to takeoff which included him visually checking the quanitity of fuel in the inboard (main) fuel tanks. The captain reported that the engine start, run-up, taxi, and takeoff were normal. He reported that during the initial climb, after the landing gear was retracted, he and the first officer both noticed a decrease in the rate of climb and airspeed. He reported the first officer lowered the nose of the airplane to maintain "blue line" and he attempted to identify the problem. He stated the engine gauges were still indicating maximum power and there was no yawing motion or rough running engine sounds. The captain stated the stall horn sounded and the first officer pitched the nose over to "...break the stall." He stated he then took over control and "...placed the airplane in a 5-10 degree bank to steer for a cornfield that appeared to be at 1-2 o'clock and just off the nose. Our altitude at this point was at best 100 feet AGL." He stated he looked at the engine gauges again and noticed a split RPM indication with the left engine being 200 to 300 RPM lower then the right. He reported he continued the landing into the corn field and the airplane began to slide to the left during the landing roll. The left wing contacted the ground and the airplane came to rest. The post accident inspection of the airplane was conducted by inspectors from the Federal Aviation Administration, Indianapolis, Indiana, Flight Standards District Office. Their inspection of the airplane revealed that Jet A fuel was present in both the main and the auxiliary fuel tanks. The captain reported they landed at the Mt. Comfort Airport at 0801 cdt after which he placed a fuel order for the airplane. Neither the captain or first officer supervised the refueling of the airplane. The fixed base operator (FBO) employee who refueled the airplane reported the pilot instructed him to put 25 gallons of fuel in the outboard fuel tanks and to completely fill the inboard fuel tanks. He stated the pilot did not specify what type of fuel should be used. He continued to state, "About an hour later I began to refuel the aircraft. Seeing that it was a bigger twin-engine aircraft I unfortunately assumed that it took Jet A, as I set myself up to refuel the aircraft the Jet A nozzle did not fit properly into the aircraft's fuel tanks. Immediately, I recalled refueling different aircraft during our recent air show that required an adapter to be fitted on the Jet A's nozzle. After attaching the adapter to the Jet A nozzle, I proceeded with the refueling." The FBO employee reported the airplane took 101.5 gallons of fuel and the fuel ticket showed the amount and type of fuel that was added to the airplane. The investigation revealed the refueler had used a rubberized adapter which fits on the end of the fuel nozzle to decrease its diameter for refueling airplanes with smaller fuel tank inlets. The airplane's wings near the fuel tank inlets were all marked "Use 100LL or 100 min grade aviation gasoline." The fuel receipt, which was signed by the first officer, did not show the type of fuel added to the airplane. The type of fuel was shown on the Master Receipt and the Invoice. The captain reported he did not drain the fuel tanks prior to the flight nor did he notice the smell of Jet A fuel when he visually inspected the main fuel tanks prior to takeoff.