Crude oil prices slipped under $88 a barrel Tuesday as traders waited to hear what Federal Reserve Chairman Ben Bernanke might say in Washington. Traders are looking for clues as to what the Fed might do to stimulate the economy. The Fed chairman is adept at dodging direct answers to questions on policy moves, but he is scheduled to testify on the economy Tuesday and Wednesday on Capitol Hill. Fed observers will be anxious to interpret his testimony. In early trading, light, sweet crude for August delivery lost 55 cents to $87.88 a barrel on the New York Mercantile Exchange. Henry Hub natural gas added 1.4 cents to $2.815 per million British thermal units. Home heating oil was up 0.36 cents to $2.8313 per gallon. Reformulated blendstock gasoline was off 0.64 cents to $2.8483 a gallon. At the pump, the national average price of unleaded gasoline was $3.406 per gallon Tuesday, up from Monday\'s $3.396, AAA said.