The world's most famous investor sold almost $4 billion US in shares in America's largest oil company late last year, but increased his stake in Canada's Suncor by four million shares, making the Calgary-based oil giant his largest single energy holding.

Warren Buffett's Berkshire Hathaway Inc. revealed in regulatory filings Wednesday that the company sold off its roughly 41 million shares of Exxon Corp. in the fourth quarter of 2014, when oil prices were cratering.

Buffett, who's strategy typically involves buying and holding stocks for years, if not decades, had only held the Exxon stake since the fall of 2013. Filings reveal he sold the entire stake to pocket some $3.9 billion some time during the fourth quarter of 2014.

Adds to Suncor stake

Exxon wasn't the only U.S. oil giant that failed to maintain Buffett's interest. Berkshire also divested a smaller stake, about a half a million shares in ConocoPhillips during the quarter.

But that's not to say that the Oracle of Omaha had soured on oil companies overall. Berkshire actually increased its stake in Calgary's Suncor, by about four million shares during the period. Buffett now owns 22 million shares in Suncor. At current prices, that's worth about $864 million Cdn.

Buffett made his first investment in Suncor in the fall of 2013, the same year he bought into Exxon.

Buffett also doubled down on another favourite of his, IBM. Berkshire added to its stake in IBM during the period by buying up 6.5 million shares in the last three months of 2014. Buffett has owned a piece of IBM for years and keeps adding to it. The stake is now up to 77 million shares, worth some $12.4 billion US.

He also more than doubled his stake in industrial equipment maker Deere & Co. to 17 million shares.

Tim Hortons owner also a Buffett buy

Buffett's moves showed more indirect love for Canada as his company bought more than eight million shares of Restaurant Brands International during the quarter — the parent company of Burger King that bought Canada's Tim Hortons in a $20 billion deal late last year.

Outside of the names listed above, Berkshire increased its holdings in Charter Communications Inc., DaVita Healthcare Partners Inc., DirecTV, Liberty Global plc, MasterCard Inc., Phillips 66, Precision Castparts Corp., Twenty-First Century Fox Inc​. Viacom Inc. and Visa Inc.

During the fourth quarter, Berkshire decreased its investments in National Oilwell Varco Inc. and Bank of New York Mellon Corp.

Investors keep a close eye on Berkshire's buying and selling, because even though the trades are only revealed well after the fact, many investors like to mimic the moves to try to keep up with Buffett's gains. Indeed, the Securities & Exchange Commission routinely grants Berkshire special permission to disclose its trades well after the fact, in order to discourage copycats.

Berkshire Hathaway shares gained 24 per cent last year.