On March 21, the U.S. regular retail gasoline price across all formulations (conventional and reformulated) averaged $4.24 per gallon (gal), and the U.S. on-highway retail diesel fuel price averaged $5.13/gal. Retail gasoline prices peaked in our weekly data on March 14 at $4.32/gal, a 22% increase from $3.53 per gallon on February 21. During the same three-week period, the average U.S. on-highway retail diesel fuel price increased 29% from $4.06/gal to $5.25/gal. Retail gasoline and diesel fuel prices have never increased so quickly on a percentage basis over a three-week period in our data (which for gasoline dates back to August 1990 and for diesel dates back to March 1994).