Gas prices up sharply in California due to 'maintenance and repairs'

[hack89]

5. This is the time of the year California switches to summer time gas formulations

which also contributes to spring price spikes.

Since then, there have been sharp spikes in fuel prices every spring as summer blends get rolled out. This is not so much because it's expensive to make the gas—the added cost per gallon is only 1 or 2 cents—but because refineries generally try to sell every last bit of winter fuel before mixing in the slightly more expensive summer batch. Sometimes they draw down the stock too far, creating shortages before the first deliveries of summer blend enter the supply chain. The return to normal blends in the fall causes a far less pronounced spike because the industry, free from summer standards, doesn't bother selling off the summer gas before mixing in the less pricey stuff.

http://www.slate.com/articles/news_and_politics/explainer/2004/04/what_is_summerblend_gas.html