Just what is summer gasoline? Twice a year, in the fall and in the spring, you hear about the seasonal gasoline transition. However, most people probably don’t understand what this actually means. AAA has provided a Top 10 list explaining the seasonal rise in gasoline prices, and summer gasoline checked in at #7:

7. The summer blend switchover. This transition from winter-blend to summer-blend fuel, a concoction that causes less smog, occurs every spring. It causes a dip in gasoline supplies as refineries in the U.S. shut down temporarily to retool their production facilities.

That's only partially correct, and is probably the extent of most people's understanding of this transition. But given that I am very keen that people should understand the energy industry, it is worth a review, and a layman's explanation. I explained the details behind this transition in Refining 101: Winter Gasoline. But let’s review some concepts.