On July 18, 1998, at 1030 eastern standard time, a Cessna 150H, N22047, sustained substantial damage during a precautionary landing near Frankfort, Indiana. The private pilot operator stated that he initiated the landing after hearing a noise and noticing a loss of engine oil pressure. Subsequent to the accident he found the oil sump plug missing, and no lubricating oil remaining in the engine. The pilot and one passenger reported no injuries. The personal 14 CFR Part 91 flight was operating in visual meteorological conditions. No flight plan was on file. The flight originated at Laporte, Indiana, at 0925 with the intended destination of Indianapolis, Indiana. After the accident an examination of the airplane revealed that the threaded drain plug from the lubricating oil sump was not present. There was evidence of oil stains in the bottom of the engine cowling, on the nose gear assembly, and the underside of the airplane. There were two oil stains under the airplane approximately 1 foot in diameter. A check of the airplane logbooks revealed that the airplane had received an inspection about six hours prior to the accident flight at which time the oil was changed. The drain plug was not found at the accident location and to date has not been recovered. The landing was made on a roadway. When the pilot encountered a pickup truck on the road he attempted to exit the road to avoid a collision and impacted crops and the terrain.