Oil prices slid Monday in Asian trading as traders took profits after last week's rally, but concerns about unrest in Nigeria and the possibility of UN sanctions against Iran were expected to support prices. Light, sweet crude for April delivery fell 7 cents to US $59.89 a barrel on the New York Mercantile Exchange, midmorning in Singapore. Gasoline fell nearly 1 cent to US$1.68 a gallon. Heating oil also slipped less than 1 cent to US $1.6767 a gallon, while natural gas rose 12.4 cents to US $6.770 per 1,000 cubic feet. On Friday, oil prices settled at $59.96 a barrel, the lowest settlement price since Feb. 17, when the contract settled at US $59.88.