LONDON (Dow Jones)--BP PLC's (BP) plan to sell $30 billion in assets to help fund its oil spill liabilities could cut the company's oil and gas output to about 3.5 million barrels equivalent a day, from just under 4 million boe a day, Chief Executive Tony Hayward said Tuesday. BP will maintain a conservative approach to its finances as long as the ultimate liability for the Gulf spill is uncertain, Hayward said. This includes keeping debt levels low, he said. The company also has no intention of drawing down the $16 billion of bank credit lines it has in reserve, said Chief Financial Officer Byron Grote. BP will publish an interim report on the causes of the Macondo well blowout that triggered the oil spill towards the end of August, Hayward said. It isn't clear when BP will be able to complete its investigation as it cannot access key evidence, notably the blowout preventer that is still on the sea bed. BP also hasn't seen important records of events on the rig from Haliburton Co. (HAL) and Transocean Ltd. (RIG). Hayward challenged other oil companies' assertions that they use different well designs to BP. The Macondo design has been used by many other companies on many other wells in the Gulf of Mexico, he said. -By James Herron, Dow Jones Newswires; +44 (0)20 7842 9317; james.herron@dowjones.com (END) Dow Jones Newswires July 27, 2010 10:40 ET (14:40 GMT)