Rating agency Moody's has downgraded BP's credit rating, adding to concerns over the impact of the continuing oil leak in the Gulf of Mexico on the company's finances.
Moody's downgraded BP's creditworthiness by three notches, following similar moves by the other two rating agencies earlier this week.
BP, which says its finances are sound, is to put aside $US20 billion for compensation payments.
The company made a profit last year of $US14 billion, down from $US25 billion a year earlier.
Moody's said the full costs of the oil spill would have a negative impact on the company's cash flow for "a number of years". As a result, it downgraded BP from A2 to Aa2.
However, it said the company's payments into the compensation fund were "manageable".
The BBC reports BP shares fell 0.6% on Friday, after climbing almost 7% a day earlier.
Earlier this week, the two other major international credit ratings agencies, Fitch and Standard & Poor's, also downgraded BP.
Standard & Poor's lowered BP's corporate credit ratings to A from AA-. Fitch Ratings downgraded it from AA to BBB.
Standard Chartered warned last week that the total cost to the company, including legal costs, could top $US40 billion.
The oil leak began after an explosion and fire on the Deepwater Horizon drilling rig on 20 April. The rig sank two days later.