BP...has accused the U.S. government of withholding evidence that may show the 2010 Deepwater Horizon oil spill in the Gulf of Mexico was smaller than federal officials claimed, a key issue in determining the oil company's liability. A reduction in the size of the spill would lower the maximum civil fine BP could be forced to pay under the U.S. Clean Water Act, a sum now estimated as high as $17.6 billion. The government is one of many plaintiffs suing BP over the April 20, 2010 explosion of the Deepwater Horizon drilling rig, which killed 11 workers and triggered the largest U.S. offshore oil spill. In a filing...with the U.S. district court in New Orleans, BP said more than 10,000 documents the government is refusing to turn over "appear to relate to flow rate issues" at the company's ruptured Macondo well...Wyn Hornbuckle, a U.S. Department of Justice spokesman, declined to comment.