With just one tweet, U.S. President Donald Trump conjured up the prospect of a global oil alliance to rescue the industry from the worst shock in history. The question is whether it evaporates just as quickly.

After the president’s social-media intervention on Thursday, oil traders are frantically assessing whether Saudi Arabia, Russia and possibly even the U.S. — the world’s three biggest producers — are poised to strike a once-unthinkable grand bargain to cut daily supplies in unison by 10 million to 15 million barrels.

It’s unclear whether it’s feasible — or even legal — for such a coalition to come together. Or indeed whether it would be enough to tame the tsunami of unwanted crude now bearing down on world markets, which could be two to three times bigger than the cut touted by Trump.