Crude oil prices rose modestly Monday morning, adding 23 cents to $104.93 per barrel on the New York Mercantile Exchange. West Texas Intermediate crude rose but gains are apt to be held in check this week because of disappointing manufacturing data from China. Reformulated blendstock gasoline was up 0.97 cents $3.013 per gallon. Home heating oil added 2.29 cents to $3.036 per gallon. Natural gas dropped 8 cents to $3.483 per million British thermal units. At the pump, the national average price for a gallon of unleaded regular gasoline was $3.631 Monday, down from Sunday\'s $3.634, the AAA Fuel Gauge report said.