Oil and gas companies drilling in the U.S. Gulf of Mexico may need to pay millions of dollars for improvements to safety valves on the seabed floor they hope never get used. The U.S. Interior Department is drafting rules for modifying blowout preventers...that are the last chance to stop an out-of-control oil well from spewing crude into the sea. Regulators are focusing on tighter rules because a unit on BP...’s leased Deepwater Horizon rig failed in 2010, leading to the worst offshore oil spill in the U.S.