NEW YORK (MarketWatch) -- Crude oil futures climbed back over the $80 a barrel level on Monday, though they remained down slightly, as a weakening in the dollar helped offset worries about monetary tightening in Asia. Crude oil for April delivery was down 28 cents, or 0.4%, at $80.40 a barrel. The more actively traded May contract was down 16 cents, or 0.3%, at $80.81 a barrel.