On January 31, 1998, about 1530 eastern standard time, a Cessna 172, N6261E, owned by a private individual, operating as a Title 14 CFR Part 91, personal flight, impacted with a tree during a forced landing near Valkaria, Florida. Visual meteorological conditions prevailed and no flight plan was filed. The airplane was substantially damaged. The private pilot was not injured. The flight had originated from Sebastian, Florida, at 1515. The pilot was on a short flight to buy fuel at Valkaria. At a cruise altitude of about 1,500 feet, the pilot reported that the engine began to sputter. He said that before he departed, "...my fuel indicators were showing, left tank between 1/2-1/4 and right just above 1/4 tank...I did not dip my tanks." About 6 miles from the destination airport the airplane's engine "sputtered." He switched to the left tank, the right tank, then back to both tanks. He tried both magnetos and the problem did not clear. The engine then was "windmilling." He could not maintain altitude so elected to make a forced landing in a field, and struck a tree with the left wing. Examination of the wreckage revealed, no fuel in either tank. Examination of the engine did not reveal any discrepancies.