Oil prices fell on Wednesday after industry data showed a surprise build in U.S. crude stocks last week as a deep freeze in the southern states curbed demand from refineries that were forced to shut. Crude stockpiles rose by 1 million barrels in the week to Feb. 19, the American Petroleum Institute (API) reported on Tuesday, against estimates for a draw of 5.2 million barrels in a Reuters poll. API data showed refinery crude runs fell by 2.2 million bpd.