DOW JONES NEWSWIRES President Barack Obama's administration sent BP PLC (BP, BP.LN) its biggest invoice yet--$51.4 million--for oil clean-up efforts in the Gulf of Mexico. The oil giant already has agreed to a $20 billion escrow fund for clean-up and other expenses related to the massive oil spill flowing out of its deepwater Macondo well. Late last week, BP's minority partner in the well, Anadarko Corp. (APC), refused to pay its share of the $20 billion fund, as it accused BP of gross negligence. Monday, the administration said it has billed BP and other, unnamed responsible parties $51.4 million, raising the total to $70.9 million. The amount includes expenses related to more than two dozen federal entities and agencies responding to the broken well, which is estimated to be leaking about 35,000 to 60,000 barrels of oil every day. BP shares were flat after hours at $30.33. The stock declined sharply during the regular session following the Anadarko news. Shares have dropped by nearly half in 2010. -By Joan E. Solsman, Dow Jones Newswires; 212-416-2291; [email protected] (END) Dow Jones Newswires June 21, 2010 19:01 ET (23:01 GMT)