OPEC has been surprisingly stable compared to historic cartels, largely due to the Saudi dominance and willingness to bear the brunt when the inevitable cheating occurred.
They're playing a different game now, though: that shale isn't going away, and the price of producing it is a ceiling on the cartel price.
*All* cartels eventually end by cheating; some just get there faster than others . . .
(And the *real* key to the Debars cartel was somehow convincing people that the least desirable gemstone, the plain white wine, was the most desirable and only thing to put in an engagement ring . . . before that, diamonds were *less* valuable than rubies, sapphires, etc. . .