On June 10, 1994, at 1230 central daylight time, a Coot A, N123AF, registered to Arthur J. Popehn of Plymouth, Minnesota, and operated by a commercial pilot, experienced a loss of engine power. During a forced landing the airplane sustained substantial damage. The pilot received serious injuries. The personal 14 CFR Part 91 flight was operating in visual meteorological conditions. No flight plan was on file. The local flight departed at 0845. According to the pilot, his attention was focused on the oil temperature and pressure gages on the newly overhauled engine. The engine had previous problems with oil leaks and the pilot stated he was attempting to determine the source of the leak. The pilot stated he was 10 miles north of Anoka County Airport when he realized that the fuel quantity gage read empty. He then descended from 5,000 feet to approximately 3,000 feet mean sea level into a southwest wind. The engine started to sputter as the airplane entered a mid-field downwind for runway 17 at the Anoka County Airport. The pilot stated that when he realized the airplane would not reach the runway, he elected to land in a pasture between a barn and a large grove of trees. He stated that during the forced landing the airplane encountered rough terrain.