There are three major refining centers on the West Coast, the Pacific Northwest (PNW), the San Francisco Bay (SFB), and Los Angeles (LA). The refineries in the PNW supply Washington, Oregon and California with gasoline. The SFB plants supply Northern California, Northern Nevada and Southern California with gasoline. Excess gasoline from the PNW and SFB is tankered to LA because there are no connecting pipelines.

The LA refineries supply product to Southern California, Southern Nevada and Arizona. Normally the PNW and SFB are long on gasoline and LA is short. Gasoline is routinely exported to Canada, Mexico and Central America from the northern refineries.

The Southern California gasoline market has been especially volatile this year. The graph below shows the spot price for California Blendstock for Oxygenate Blending (CARBOB) for the Los Angeles and San Francisco markets, relative to the New York Mercantile Exchange (NYMEX) price.

Refining is the key link in the global supply chain extending from production of crude oil to end-use consumption of refined products. Crude oil as it exists at the wellhead is essentially worthless; a crude oil's value is in the value of the products made from it. 

Petroleum products produced from crude oil by refineries, meet more than one third of global energy demand and more than 95% of energy demand in the transportation sector. Refined products range from LPG (propane) - the lightest - through gasoline, jet fuel, and diesel down to asphalt and fuel oil - the heaviest. Light products - primarily the transportation fuels and petrochemical feedstocks - are more valuable than heavy products, such as fuel oil and asphalt. In the U.S., light products (mainly gasoline and diesel fuel) make up more than 75% of the product barrel.