Kenneth Feinberg takes over today the gargantuan task of distributing the $20 billion BP is setting aside to reimburse victims of the Gulf oil spill. He has said he will approve compensation claims by relying on precedents set by state and federal law. But law professors following the issue say it is unclear just how Feinberg will interpret a key legal doctrine called “proximate cause,” which will determine exactly who gets a slice of the compensation fund.