Billionaire investor T. Boone Pickens sold his energy equity fund’s stake in BP Plc during the second quarter, exiting its largest holding by market value.

Pickens’s Dallas-based BP Capital Management LP sold 452,111 of the company’s American depositary receipts, or ADRs, in the three months ended June 30, according to a filing with the U.S. Securities and Exchange Commission. The stake in London-based BP had been valued at more than $20 million at the end of March.

The oil and natural-gas producer’s ADRs, which trade on U.S. markets and represent six ordinary shares, fell 9.9 percent during the quarter. The company reported a $1.4 billion net loss for the April-to-June period, compared with profit of $5.7 billion a year earlier, as it wrote down the value of U.S. assets and output dropped.

Pickens began acquiring a stake in BP after its Macondo well in the Gulf of Mexico exploded in April 2010, resulting in the biggest offshore oil spill in U.S. history.

The value of Pickens’s equity holdings fell 25 percent to $130.7 million as of June 30, from $174.5 million at the end of the first quarter, according to the filing.

The fund added stakes in several U.S. oil and gas producers during the past quarter, including McMoRan Exploration Co., Anadarko Petroleum Corp., Apache Corp., EOG Resources Inc., Pioneer Natural Resources Co., Quicksilver Resources Inc. and Southwestern Energy Co.

Cutting Stakes

Pickens sold stakes in the world’s two largest oilfield service companies, Schlumberger Ltd. and Halliburton Co., and reduced holdings in National Oilwell Varco Inc. and Weatherford International Ltd. He also sold all of BP Capital’s stakes in power utility owner Exelon Corp. and Canadian oil company Suncor Energy Inc.

The fund’s stake in SandRidge Energy Inc. was cut to 278,479 shares from about 1.2 million. The U.S. energy producer’s chairman and chief executive officer, Tom Ward, was a co-founder of Chesapeake Energy Corp., which Pickens exited completely during the second quarter.

Pickens said in May he had sold his remaining stake in Chesapeake amid a plunge in gas prices and after potential management conflicts were raised about CEO Aubrey McClendon.

Money managers who oversee more than $100 million in equities must file a Form 13F with the U.S. Securities and Exchange Commission within 45 days of each quarter’s end to show their U.S.-listed stocks, options and convertible bonds. The filings don’t show non-U.S. securities or how much cash the firms hold.