Oil prices have tumbled as much as 5% , with US crude falling to its lowest level since February. Crude oil futures prices shed more than 5% Thursday, plunging to their lowest level since February in a broad market sell-off spurred by intensifying fears that the world''s major economies are stalling. Light, sweet crude futures for September delivery settled down $5.30, or 5.8%, to $86.63 on the New York Mercantile Exchange on the contract''s lowest settle since Feb. 18.