There's insufficient supply along the entire West Coast of North America, so if something happens to upset the balance, such as a refinery shutdown, it causes prices to spike rapidly.
Back in March, the Philips 66 refinery near Los Angeles, California shut down due to a fire at the refinery. That refinery had a capacity of about 139,000 barrels a day, which makes it a fairly large refinery along the entire Western US.
Adding to the chaos was that there was also another fire and explosion at the Exxon Baytown, Texas refinery at about the same time which can process 560,500 b/d.
Also, in April, a number of Californian refineries shut down due to planned maintenance or mechanical breakdowns; those included:
- Chevron El Segundo refinery (290,500 b/d); maintenance
- Marathon Los Angeles refinery (383,000 b/d); maintenance
- Valero Wilmington refinery (87,000 b/d); breakdown
- Chevron Richmond refinery (260,000 b/d); breakdowns causing heavy flaring
- Valero Benicia refinery (149,000 b/d); breakdown leading to heavy maintenance
Adding to the issues was that refineries were also switching from the winter-blend to the summer blend; causing disruptions in supply to allow for the switch over to occur.
These refineries are now back up and running, meaning supplies of refined fuel have stabilized, causing prices to drop. Coupled with a depressed price for crude oil, this has pushed gas prices back down from their highs earlier this year.
Normally, you don't see this many refineries go down at about the same time; maintenance work is usually carefully planned to ensure that the shutdown does not occur when other nearby refineries are shut down to ensure a steady flow of product.