Promised cuts enabled OPEC to talk up oil prices over the past few months (intended to boost the value of their planned Aramaco IPO in 2018), but the downside is that higher prices encourage higher production and ultimately a round trip back to lower prices. U.S. oil production is growing again as shale comes out of hibernation faster than OPEC had hoped. See US Shale’s Great Reawakening:
It was always going to be a matter of when and not if OPEC would have to start grappling with the return of shale, and it looks like that time had already come even before it started supporting oil prices again. The big question is to what degree will the group and its members comply with what they said they’ll do, and how much extra boost that will give to the U.S. shale oil industry.