ST. PETERSBURG—The Organization of the Petroleum Exporting Countries met Monday with big oil-producing allies such as Russia, wrestling with a difficult fact: They are pumping too much crude. OPEC, the 14-nation cartel, and 10 big non-OPEC producers agreed last year to reduce their petroleum output by almost 1.8 million barrels a day—nearly 2% of global oil supply—to draw down a global glut that keeps prices low. But prices have…