When Warren Buffett buys shares of any company, it makes news. And the legendary investor has been busy buying lately. Berkshire Hathaway (BRK.A 0.48%) (BRK.B 0.44%) added to its positions in several companies in the third quarter of 2022.

But what doesn't always receive as much attention is which companies Buffett influences the most -- the ones where Berkshire owns the largest stakes. Buffett now owns 20% or more of these five companies.

Warren Buffett with people in the background.

Image source: The Motley Fool.

Long-time positions

There are four companies in Buffett's portfolio of which Berkshire has owned at least 20% for quite a while. Buffett first bought shares of American Express (AXP 1.53%) way back in 1964. He made a boatload of money from the investment but sold the stock within a few years.

Buffett regained an interest in AmEx in 1993. It's now Berkshire's second longest-held position. AmEx ranks as the fifth largest holding in the giant conglomerate's portfolio. But although Berkshire has a 20.3% stake in American Express, its agreement with the company is to always vote most of its shares in accordance with the recommendation of AmRx's board of directors as long as Stephen Squeri is CEO.

Berkshire has a 40.1% stake in Davita (DVA 0.06%). It owns more of the dialysis services provider than any other company that it isn't a Berkshire subsidiary. Buffett first invested in Davita in 2011. 

If you look at the list of Berkshire Hathaway's subsidiaries on the company's website, you'll find Kraft Heinz (KHC 1.67%). However, Berkshire's stake in the food company is actually only 26.6%. Buffett initially bought H. J. Heinz in 2013 and went along with Heinz's merger with Kraft Foods in 2015.

Berkshire owns shares of several Liberty Media stocks. Its biggest position among the group is in Liberty Media Corp Series A (LSXMA -0.62%) with a 20.6% stake. Berkshire also owns a 19.8% stake in Liberty SiriusXM Group and a 3.7% stake in Formula One Group, both of which are Liberty Media tracking stocks.

Bulking up

During the first half of 2022, Berkshire bought around 17% of the outstanding shares of Occidental Petroleum (OXY 0.60%). But Buffett kept on buying the oil stock during the third quarter. Berkshire now owns a 21.4% stake in Occidental.

Don't be surprised if Buffett buys even more. In August, Berkshire secured approval from the Federal Energy Regulatory Commission (FERC) to acquire up to 50% of Occidental. 

Best bets?

Which of these high-stake Buffett stocks are the best bets for regular investors? I think Occidental ranks as the best near-term play. 

Berkshire's likely further purchases of Occidental stock could push the share price higher. The tailwinds from high fuel prices will probably continue as well. Despite its huge gain of nearly 150% so far this year, Occidental's shares still trade at 10.4 times expected earnings. Its enterprise value-to-free-cash-flow multiple also stands at an attractive level of 7.0.

However, oil stocks like Occidental will probably become increasingly riskier over the long term. The shift to renewable energy sources will take years, but it's inevitable. Even though Occidental is investing in carbon capture projects and other clean energy efforts, the stock might not be as great of a pick 10 years from now as it is today.

So which of the other stocks in which Berkshire owns stakes of 20% or more is the best long-term pick? My vote goes to American Express. 

Sure, AmEx stock is down year to date. However, it's easily beating the overall market. More importantly, the company's long-term prospects remain bright. Credit card use should continue to increase. Businesses, in particular, will almost certainly continue to flock to American Express.

Buffett has made a lot of money through the years from his investment in AmEx. I think that he will continue to do so.