A pal of mine
US Memorial Day, which is the last Monday of May each year (next Monday, May 25 this year), is the start of US summer driving season. School's out, the weather is good and everyone takes their vacation. With gasoline ($2.30/gal) a lot less expensive than this time last year ($3.20/gal), driving is expected to be higher than last year. Seasonality of all types is discussed in Oil 101.
(Source: DOT and Oil 101 Page 285 Fig 13-2)