Oil prices fell below $81 a barrel Tuesday in Asia, the Associated Press reported. Benchmark crude for September delivery was down 56 cents at $80.92 a barrel at late afternoon Singapore time in electronic trading on the New York Mercantile Exchange. The contract rose 78 cents to settle at $81.48 on Monday. In other Nymex trading in September contracts, heating oil fell 0.88 cent to $2.1450 a gallon, gasoline dropped 0.92 cent to $2.1095 a gallon and natural gas slid 1 cent to $4.299 per 1,000 cubic feet. Brent crude was down 53 cents at $80.46 a barrel on the ICE futures exchange.