A curb on oil production may be hard for Opec to police

Oil traders and investors cheered last Wednesday’s landmark deal to curtail oil production. But history shows compliance with past accords to be patchy at best. Even if countries stick to their output caps, those that won exemptions could make the collective target all but unreachable if they boost production. The difficulty of monitoring non-Opec cuts adds a further layer of uncertainty.

“You do have a problem with production compliance for sure,” said Olivier ...