On April 8, 2002, at 0850 central daylight time, a Rockwell International 500-S, N8536, registered to and operated by Air Carriers, Inc., landed in a field following a loss of power in both engines in Jackson, Alabama. The on-demand air taxi flight was operated under the provisions of Title 14 CFR Part 135 with an instrument flight plan filed. Visual weather conditions prevailed at the time of the incident. The commercial pilot was not injured, and the airplane was not damaged. The flight departed Bessemer, Alabama, at 0750 on April 6, 2002. The pilot stated she completed her "usual preflight of the aircraft, which included checking engine oil and fuel," and she stated, "the fuel was topped off." Approximately 20 minutes after takeoff, the flight was cruising at 8,000 feet msl. At this time the fuel gauge showed 80 gallons in the fuel tank. Approximatelt 10 minutes later, the fuel gauge showed 50 gallons of fuel in the tank. The pilot elected to continue the flight to the planned destination of Mobile, Alabama. As the flight approached Jackson, Alabama, both engines sputtered, and the pilot performed the fuel emergency checklist. The pilot turned on the fuel boost pumps and retuned the mixture levers to full rich. The pilot reported the engine out problem to air traffic control, and requested a heading to the nearest airport. The pilot reversed her heading and statred a descent from 8000 feet. The airplane descended through the clouds and broke out about 2,800 feet msl. The pilot saw only trees and rolling hills, however the pilot located a pasture and landed the airplane without further incident. The pilot stated, "both engines were stopped. At that time I exited the airplane and did notice the fuel cap was off, still attached to the chain." Examination of the airplane found the fuel cap was unsecured and hanging by its chain. There was no fuel in the fuel system, and there was no evidence of fuel splatter on the wing, fuselage, or tail surfaces. The wing skin around the fuel fill port and chain attachment displayed no scratches nor dents. The fuel cap chain assembly was of the type designed to break free at 20 knots airspeed in the event a fuel cap is left unsecured, and the airplane was equipped with a non-siphoning fuel fill port. The pilot reported no mechanical malfunction, and no evidence of defect was observed with the fuel cap chain.