(Reuters) - Warren Buffett's Berkshire Hathaway Inc (BRKa.N) on Friday said it boosted its stake in cable TV operator Charter Communications Corp (CHTR.O), and signaled it may have another large investment planned after agreeing to buy Precision Castparts Corp PCP.N in its largest-ever purchase.
Berkshire also appeared to have shed its stakes in oilfield equipment provider National Oilwell Varco Inc (NOV.N) and refiner Phillips 66 (PSX.N) in the second quarter, as the oil industry struggles with falling prices.
The changes were disclosed in a U.S. Securities and Exchange Commission filing detailing Berkshire's $107.2 billion U.S. stock portfolio on June 30.
Berkshire kept some details about its holdings confidential. The SEC sometimes lets the Omaha, Nebraska-based company delay disclosures of new stakes so Buffett can build them quietly, rather than have investors piggyback on him before he finishes.
Friday's filing suggests that only a small percentage of the $3.09 billion of stock that Berkshire bought in the quarter went to companies it already owned.
Berkshire held 8.51 million shares of Charter worth $1.46 billion on June 30, up from 5.98 million shares on March 31.
Berkshire reported lower stakes in conglomerate Chicago Bridge & Iron Co (CBI.N), media company Viacom Inc (VIAB.O) and Wabco Holdings Inc (WBC.N), which sells braking and suspension systems for commercial vehicles.
It swapped most of what was once a much larger Phillips 66 stake for a chemicals business in February 2014.
Friday's filing did not disclose who made which Berkshire investments. Smaller investments are often made by Todd Combs and Ted Weschler, who may eventually succeed Buffett as chief investment officers.
Combs invested in Precision Castparts before Berkshire said on Monday it would buy the aerospace parts maker. The transaction valued that company at $32.3 billion.
Other prominent investors such as Jana Partners and Davis Selected advisers bought Precision Castparts during the quarter.
Wells Fargo & Co (WFC.N) remained Berkshire's biggest stock holding.
Kraft Heinz Co (KHC.O) became Berkshire's second-biggest holding last month, when H.J. Heinz Co bought Kraft Foods Group Inc. That transformed Berkshire's 52.5 percent stake in Heinz into a 26.9 percent stake in Kraft Heinz.
Berkshire owns more than 80 businesses, including the BNSF railroad, Dairy Queen ice cream and Geico car insurance. Buffett, who turns 85 on Aug. 30 has run Berkshire for 50 years.
Reporting by Jonathan Stempel in New York; Editing by Dan Grebler; editing by James Dalgleish