Envoys for Iran and the United States have engaged in four rounds of talks. But exactly what a deal would look like remained unclear.

US President Donald Trump said on Thursday that Washington is “very close” to reaching a nuclear deal with Iran after Tehran “sort of” agreed to its terms.

The prospect of a nuclear deal between the U.S. and Iran contributed to the biggest daily drop in oil prices so far this month. But the deal, and a subsequent lift in global oil supplies, are not a sure thing.