Seasonality is a pattern that repeats on a yearly basis. Analyzing seasonal trends allows us to have a better understanding of oil consumption. Crude oil is refined into gasoline and distillate so the seasonal trends in crude inventories are in line with demand for gas and distillate. Seasonal peaks usually appear in April, May and November; troughs in January and September. The peak and troughs of crude inventories are roughly M-shaped.

During the first upleg from Feb to May, inventories increase because refineries are preparing for the summer driving season to come.

From June to August, the first downleg, demand for oil surges because people travel a lot in the summer. Refineries pick up pace to produce gas and distillate; crude inventories decrease.

From September to November, inventories build up as refineries shut down for maintenance.

During the winter, demand for heating oil (distillate) surges; crude inventories decrease.