OPEC on Wednesday trimmed its forecast for growth in oil supply from the United States and other producers outside the wider OPEC+ group this year and said it expected lower capital spending following a decline in oil prices.

Wall Street veered lower before the opening bell Thursday and oil prices fell more than $2 a barrel as optimism over a possible U.S.-Iran nuclear deal rose. Futures for the S&P 500 and Dow Jones Industrial Average each fell 0.

The prospect of a deal over Iran’s nuclear program saw oil fall sharply on Thursday. The reality is that Tehran has relatively little extra crude that it can bring back — but it could arrive in a market that’s gearing up for surplus.