As oil and gas prices have tumbled, Exxon and Shell have been forced to retreat. With oil barely above $30 a barrel, they’re cutting spending, including some costly, high-risk mega-projects. This may not be the best time to be bigger than big. The $64 billion tie-up of Royal Dutch Shell Plc with BG Group Plc and the steady growth of Exxon Mobil Corp. are creating a new league of two: the ultramajors. Executives at smaller companies are even starting to joke that Chevron Corp., Total SA, BP Plc, ConocoPhillips and ENI SpA are merely the mid-cap sector of Big Oil. But as oil and gas prices have tumbled, Exxon and Shell have been forced to retreat. With oil barely above $30 a barrel, they’re cutting spending, including some costly, high-risk mega-projects. Shell abandoned construction of the 80,000 barrel-a-day Carmon Creek oil sands project in Alberta, Canada, last year after […]