President Donald Trump said Monday the U.S. is “looking” to add as many as 75 million barrels of oil to the Strategic Petroleum Reserve, after an historic day for markets that saw crude prices turn negative.

The soon-to-expire May contract CL.1, -3.81% US:CLK20 for West Texas Intermediate crude on the New York Mercantile Exchange traded, and closed, in negative territory, as MarketWatch reported.