LONDON — British energy giant BP PLC on Tuesday reported a 67 percent drop in third-quarter profit as it took an additional charge of $7.7 billion to cover costs related to the worst oil spill in U.S. history.

Net income at the firm still troubled by its role in the Gulf of Mexico incident last April tumbled 67 percent to $1.79 billion in the quarter.

On a sequential basis, however, the results marked BP’s return to profit after it posted a $17.2 billion loss on charges of $32.2 billion in the second quarter.

The additional $7.7 billion charge stemmed in large part from the later-than-expected capping of the ruptured well, BP said Tuesday. It brought the company’s estimate of the likely cost of the spill to $39.9 billion.

Setting aside the rising bill, BP’s operational results actually improved year on year. Adjusted replacement cost profit, which strips out one-time items and changes in the oil price, rose 18 percent to $5.5 billion, topping the consensus forecast of $4.6 billion.

Some of BP’s biggest rivals, including Exxon Mobil Corp., Royal Dutch Shell PLC and Total SA, delivered large profit increases this quarter on the back of a 13 percent rise in oil prices.