When the Deepwater Horizon rig exploded in the Gulf of Mexico in 2010, triggering the largest-ever oil spill in the US, all eyes turned to BP Plc, the British company behind the drilling. But BP wasn’t alone in the project. Among its partners was Japan’s Mitsui & Co., which held a 10% stake. Little-known outside the natural-resources industry, Mitsui is part of a group of five Japanese companies that invests in energy and commodity projects around the world. They are Japan Inc.’s commodity arm with interests in everything from coal mines in Australia to oilfields in Oman and wheat silos in Canada. For years, it has been a monotonous business few paid attention to. But now, thanks to a yearlong period of sky-high raw-material prices, the Japanese traders are squeezing more cash than ever from those projects, becoming among the biggest – though under the radar — winners of the 2022 inflation boom. Add the profits from buying and selling the commodities, and net income is at a record.The Japanese traders may be largely unknown, but one of their top investors — and beneficiaries — is quite prominent: Warren Buffett.The Oracle of Omaha has turned a two-year old bet on the five companies – known collectively as the sogo shosha, or general trading companies — into gold, recently upping the wager by increasing his stake in each. Today, Buffett is the third-biggest shareholder in Mitsui and a leading investor in its compatriots Mitsubishi Corp., Itochu Corp., Sumitomo Corp. and Marubeni Corp. With some differences, the five follow the same business model: take stakes in natural-resources projects, trade the commodities they produce, and use the cash to slowly diversify.Berkshire Hathaway Inc., Buffett’s investment vehicle, first disclosed the investment in the sogo shosha in August 2020, with 5% stakes in each worth a total of $6 billion at the exchange rate of the day. Those positions have gained more than 50%, even when accounting for the depreciation of the yen against the dollar. Two months ago, Berkshire disclosed the purchase of more shares, bringing the stake to about 6.5% — or roughly $12 billion at today’s exchange rate.