(Adds BP's oil collection rate for first half of Monday.) 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 said later Monday that during the first 12 hours of the day it collected 8,410 barrels of oil and flared about 5,015 barrels, an improvement on is previous half-day rate. The company has been under intense pressure to successfully contain the spewing oil, which began in April when a deepwater drilling rig exploded and sank. The company's repeated failures at a temporary solution to patch the leak heightened scrutiny of its response, and it is still working on a permanent fix to the well. BP's American depositary shares were down 2 cents after hours at $30.31. 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; joan.solsman@dowjones.com (END) Dow Jones Newswires June 21, 2010 19:14 ET (23:14 GMT)