Reuters: An internal BP document released by a U.S. lawmaker estimated that a worst-case scenario rate for the Gulf of Mexico oil spill could be about 100,000 barrels per day, far higher than the current U.S. figure. Shares in the oil giant, which have nearly halved in value since an explosion at an oil well in the Gulf of Mexico on April 20, slid 4.3 percent in early trade. The group said the cost of its response to the spill had hit $2 billion and it had paid out $105 million in …