Is it a floor, or a ceiling?

Competitive market conditions would therefore dictate that Saudi Arabia and other low-cost producers always operate at full capacity, while US frackers would experience the boom-bust cycles typical of commodity markets, shutting down when global demand is weak or new low-cost supplies come onstream from Iraq, Libya, Iran, or Russia, and ramping up production only during global booms when oil demand is at a peak.

Under this competitive logic, the marginal cost of US shale oil would become a ceiling for global oil prices, whereas the costs of relatively remote and marginal conventional oilfields in OPEC and Russia would set a floor. As it happens, estimates of shale-oil production costs are mostly around $50, while marginal conventional oilfields generally break even at around $20. Thus, the trading range in the brave new world of competitive oil should be roughly $20 to $50.

Makes sense to me.

[Update a few minutes later]

I’ve long said that oil over a (inflation adjusted) hundred dollars a barrel was unsustainable. This would seem to validate that.