Crude oil prices slipped under $91 per barrel Tuesday as equities were flat in Asia and Europe and early gains faded in New York. The dollar index rose slightly, putting pressure on commodities. West Texas Intermediate crude oil for November delivery shed 51 cents in late trading to $90.86 per barrel. Natural gas added 1.8 cents to $2.942 per million British thermal units. Home heating oil lost 0.88 cents to $3.0975 per gallon. Reformulated blendstock gasoline shed 2.12 cents to $2.8012 per gallon. At the pump, the average price for a gallon of regular unleaded gasoline was $3.81 per gallon, up from Monday\'s $3.808, AAA reported.