For the world’s biggest oil traders, it feels like a return to the 1980s when earnings were diluted by an abundance of crude. After three decades of stellar expansion and booming revenues, profit margins at Vitol, Glencore, Trafigura, Gunvor, Mercuria and other merchants have been squeezed by a market again awash with crude and amid stiff competition from national oil firms. A raft of high-profile U.S. probes into trading activities are also shaking up the business, echoing the transformation that followed the 1983 U.S. indictment of Marc Rich, the godfather of global oil trading. (Graphic: Oil trading profits link: tmsnrt.rs/31K1R1a ) Veteran executives, many of whom learned the trade in the Marc Rich era, say only the fittest firms […]