U.S. gasoline and diesel crack spreads (the difference between the price of crude oil and the wholesale price of the petroleum product, which are used as estimates of refinery margins) diverged sharply in March as the Covid shutdown happened.  Cars drove fewer miles = less gas needed.   Lower gasoline demand pulled gasoline crack spreads down.  During the same period, demand for diesel fuel remained relatively strong, which contributed to a sharp increase in diesel crack spreads.  In April, diesel yields increased as demand fell, reducing the diesel crack spread, while gasoline demand began to increase.  Since then, gasoline and diesel crack spreads in the U.S. Gulf Coast (home to about half of the U.S. refining capacity) have stabilized and moved together.