A two-year battle for global oil supremacy that pit Saudi Arabia, head of the powerful oil cartel, against upstart U.S. shale producers left them both badly wounded but with each side claiming victory. The Organization of the Petroleum Exporting Countries deal last month to cut oil production has sparked a powerful rally after crude prices had fallen in half over the past two years. That slide followed OPEC’s decision in late 2014 to maintain production levels, despite a global glut. For U.S. shale companies, it was two years of shrinking profits and mass layoffs as dozens of producers scaled back output or sought bankruptcy protection. But the survivors became much more efficient and are now eager to grab market share at their foreign competitors’ expense. “Definitely, the U.S. is going to win the next two years because OPEC is cutting and U.S. shale is taking off,” said Scott Sheffield, […]