BHP Billiton rose 3p to 377p on the back of a drilling report from its Neptune 5 appraisal well in the Gulf of Mexico. The find was said to be significantly bigger than those recorded in nearby wells. Meanwhile, workers at the Escondida copper mine in Chile, in which it has a near-60% stake, have gone on strike. The threat of industrial action at the world's biggest copper mine had driven up the price of copper to a 30-month high.