The promise of production cuts from OPEC and its partners sent oil rallying in 2016. Now traders want proof they’re delivering on those vows. It won’t come easy. The challenge: Building a coherent picture from the morass of data that emerges at each step along the process, from the wellheads where the oil is produced, to the tankers that carry it, and the depots that store it. Unlike in the U.S., where output is published weekly, members of the Organization of Petroleum Exporting Countries can take months to disclose their production. Beyond that, their data can be at odds with independent surveys, and countries have been known to cheat on such deals. With a rising U.S. rig count offering a bearish undertone, each new hint on the accord’s implementation can be expected to swing prices. “The market could be whipsawed more by data and headlines than in the past,” […]