Oil prices moved slightly higher Friday morning, with outside influences keeping gains in check, a barrel of crude holding to less than $91. Overnight, the price of West Texas Intermediate for July delivery added 33 cents to $90.74 per barrel. Natural gas for June delivery lost 3.8 cents to $2.609 per million British thermal units. Home heating oil added 0.25 cents to $2.8282 per gallon. Gasoline futures off 0.16 cents to $2.8177 per gallon. At the pump, the national average price of unleaded gasoline dropped 1 cent to $3.666 per gallon from Thursday\'s $3.676, AAA said.