DOW JONES NEWSWIRES Standard & Poor's Ratings Services lowered its rating on BP PLC (BP, BP.LN) by two notches, its second downgrade on the oil giant this month, citing higher oil leak estimates and "intense political pressure in the U.S.," its largest market. The downgrade reflects the ratings agency's opinion of the challenges and uncertainties that BP continues to face in the aftermath of an ongoing spill in the Gulf of Mexico, which was triggered by an explosion on April 20 that destroyed an oil rig, killing 11 crew workers. BP has been scrambling to cap the well and contain the spill. "These challenges and uncertainties include the difficulties BP is experiencing in containing the spill as well as the ultimate extent of the pollution, the consequences for BP of ongoing official investigations, and the implications of these investigations for the magnitude and timing of further cash payments by BP," said analyst Simon Redmond. S&P said questions raised during a U.S. Congressional hearing Thursday, as well as the higher oil leak estimates announced earlier this week, increased its estimated short- and long-term potential liabilities for BP. U.S. lawmakers blasted BP's Chief Executive Tony Hayward on Thursday at his first appearance before Congress since the oil-rig explosion. The company is reportedly to contribute $20 billion of assets to a specifically established claims fund, although these payments don't amount to a cap, S&P said. At the same time, BP has also reportedly agreed to increase its cash resources and to this end has agreed to suspend dividend payments, reduce capital investments and accelerate asset disposals. On their own, S&P views these steps to increase cash resources as credit supportive although, in the circumstances, it said it was of the view that "their benefit is less significant than the negative effect on credit that has arisen." As a consequence, S&P lowered the company's rating to A, which is five notches into investment-grade territory, and kept the ratings on watch for further downgrade. S&P lowered the rating by one notch earlier this month, while its peers -- Moody's Investors Services and Fitch Ratings -- have also downgraded their ratings on BP and warned of further downgrades. BP's American depositary shares closed down 0.4% to $31.71 in recent trading. The ADSs have slumped 45% this year. -By John Kell, Dow Jones Newswires; 212-416-2480; john.kell@dowjones.com (END) Dow Jones Newswires June 17, 2010 16:06 ET (20:06 GMT)