Billionaire Warren Buffett has added to his energy bets, saying in a filing late Friday that Berkshire Hathaway (BRK.A) has amassed an almost 11 percent stake in oil refiner Phillips 66 (PSX) valued at around $4.5 billion, The Deal reports. The almost 58 million share stake replaces a previous investment he had in the company before he traded it for a pipeline additives business for his Lubrizol Corp. unit in 2013 in a deal valued at $1.4 billion. The Omaha-based conglomerate didn't mention the stake in a filing with the SEC earlier this month but in May reported that it owned 7.5 million shares in the Houston company as of late March. Berkshire couldn't be reached to comment on the latest investment. TheDeal's Tatjana Kukarni reports from New York.