On the cusp of trial over the catastrophic 2010 oil spill in the Gulf of Mexico, phalanxes of lawyers, executives and public officials have spent the waning days in settlement talks. Holed up in small groups inside law offices, war rooms and hotel suites in New Orleans and Washington, they are trying to put a number on what BP and its partners in the doomed Macondo well project should pay to make up for the worst offshore spill in U.S.