According to the agency's analysis, the phenomenon can roughly be traced to early 2015, when an explosion at Exxon Mobil's Torrance refinery prompted state officials to order the company to shut down the refinery until it could demonstrate safe operation. While the ensuing outage at that refinery only lasted about a year and a half, the commission said spiking prices at the pump in California "remained well after the restoration of normal operations at Torrance."
Since 2015, the analysis found — after accounting for the state's additional taxes and other program costs — that price increases have ranged between 17 cents and 24 cents per gallon.
The commission said those price increases may be due, in part, to some oil companies charging more than others for the same product.
"While this practice is not necessarily illegal," the report says, "it may be an effort of a segment of the market to artificially inflate prices to the detriment of California consumers."
The analysis found a number of other reasons for the continued differences between California prices and the U.S. average, including crude oil prices and other recent refinery outages.
Read the full analysis: