For years, the secretive club of the world’s largest commodities traders thrived on volatility and sometimes tiny price differences in the raw materials they trade—styling themselves as nimble middlemen able to profit whether markets were rising or falling. These days, many outfits are very different animals and that’s causing unusual pain amid today’s commodities-market rout. During a decade of booming commodities prices, many of these trading firms put billions of dollars into mines, pipelines and storage terminals. Those bets were supposed to help their traders understand supply and demand, while providing their trading floors with a ready source of supply. But they also made them more exposed to falling prices in markets in which they have built up a physical presence. Just how much, however, is difficult to gauge, since many of the biggest traders are still privately held and disclose little. Even the trading floors of big, publicly […]