Marathon Petroleum Corp., Phillips 66 and Valero Energy Corp. are some of the U.S. refiners that cash in when crude costs fall faster than fuel prices. Some grades of American crude are trading at record discounts to Brent, the international benchmark, opening up huge opportunities for refiners to profit.

“As refiners cut runs to offset weaker demand and global storage starts to fill up, we are witnessing a material widening in differentials for inland and coastal grades,” Manav Gupta, an analyst at Credit Suisse Securities (USA) LLC, wrote in a note to investors on Monday. Widening differentials “have historically favored refiners relative to other energy sub-sectors.”

Refiners in the S&P 500 Index rose as much as 5% on Monday. PBF Energy Inc., which is not a member of the refiners’ index, climbed 18% after telling investors it would suspend dividends, cut capital spending, and put more than half a billion dollars in assets up for sale.

Despite Monday’s advance, the refining sector is still down more than 50% since the end of 2019 as the Covid-19 outbreak isolated millions of people and shut down massive swaths of the global economy.

“We are now turning more positive” after staying neutral or negative on refiners for nearly two years, Brad Heffern, an analyst at RBC Capital Markets LLC, wrote in a note to clients. “Benefits from lower crude prices and oversupply are likely underappreciated.”