HOUSTON/LONDON — BP Plc will face a maximum fine of $13.7 billion under the Clean Water Act for its Gulf of Mexico oil spill, several billion dollars less than feared, after a judge ruled that it was smaller than the US government claimed. The ruling by federal magistrate Carl Barbier put the size of the worst offshore spill in US history in 2010 at 3.19 million barrels. That was well below the government's estimate of 4.09 million barrels, which could have led to penalties of up to $17.6 billion. BP's stock rose 2.4 percent in London by 0920 GMT on Friday, outperforming the broader energy index, as investors worried about the size of potential penalties breathed a sigh of relief. "The ruling is a step in the right direction of what appears set to be a long and hard-fought legal battle," Barclays said in a research note. – Reuters