Crude oil prices slipped back to $90 per barrel Friday. On the New York Mercantile Exchange, West Texas Intermediate crude oil for November delivery shed $1.68 cents to $90.03 per gallon. Natural gas prices added 0.2 cents to $3.408 per million British thermal units. Home heating oil lost 3.34 cents to $3.155 per gallon. Reformulated blendstock gasoline gained 0.28 cents to $2.9457 per gallon. At the pump, the average price for a gallon of regular unleaded gasoline was $3.789 per gallon, up from Thursday\'s $3.784, AAA reported.