Why the West Coast pays more

The West Coast pays the highest diesel prices in the country, and California pays the most of all. Three things stack up to do it: a stricter state fuel specification, the highest state fuel taxes and fees in the nation, and a refining map that leaves the region supplying most of its own fuel. Each one adds to the price, and the worked example below measures the gap they open over the Gulf Coast this week.

The live numbers. In the latest EIA weekly survey, California diesel is at $8.076/gal, the West Coast (PADD 5) at $7.272/gal and the rest of the West Coast without California at $6.575/gal, against a US average of $6.292/gal. The California and West Coast pages track each gap to the US average week by week, and the West Coast page also tracks its gap to the Gulf Coast.

The CARB fuel spec

California requires CARB diesel, a tighter specification than the federal ultra-low sulfur diesel sold in the rest of the country, set by the California Air Resources Board. It holds down aromatics and sulfur and sets a lubricity standard, and fewer refineries are set up to make it. A smaller pool of qualifying fuel is harder to top up quickly when supply runs short, which is part of why the California price both sits higher and jumps faster than the national number.

Taxes and fees

California levies the highest state diesel taxes in the US: 92.9 cents a gallon in state taxes and fees in EIA's July 2026 table, against a 35.9-cent average across the states and 79.2 cents in Illinois, the next highest. Its state diesel excise tax rose to 48.2 cents a gallon on July 1, 2026, per the California Department of Tax and Fee Administration, and most of the rest is its 13% state sales tax on diesel. On top of both, EIA notes, the costs of the state's Low Carbon Fuel Standard and cap-and-trade programs land in the pump price as well. All of it rides inside the retail number the survey records.

The island effect

Geography does the rest. EIA describes the West Coast liquid fuels market as relatively isolated and largely supplied by in-region refinery production, with few pipelines linking it to the Gulf Coast. When a West Coast refinery has an outage, the replacement supply has to come by ship from far away, which is slow and costly. So a single refinery problem can tighten the regional market and send prices up fast, in a way a well-connected region would shrug off.

The isolation cuts deeper in California, where only a handful of refineries are set up to make the CARB spec at all. With a short bench, planned maintenance or an unplanned outage at any one of them pulls a meaningful share of supply offline, and there is no quick pipeline backfill. It is not only a California story, though. The West Coast reported without California, PADD 5 minus the state and its own line in the chart above, still tends to run above the US average, which is the tell that the isolation and the regional cost base are doing work on their own, before California's spec and taxes are added on top.

Worked example: the gap, measured

The spread is on the live charts above. For the week of Nov 2, 2026 California diesel was $8.076 a gallon against a US average of $6.292, $1.78 over the national number, and the West Coast (PADD 5) ran $1.36 a gallon over the Gulf Coast (PADD 3). That gap is the CARB spec, the taxes and the island effect stacked together, and the record shows how persistent it is. California sat above the US average in 99.0% of the 1,636 weekly surveys from Jul 3, 1995 through Nov 2, 2026, and its annual average topped the national one in every one of the 30 full years from 1996 through 2025. The West Coast's annual average topped the Gulf Coast's in every one of the 30 years between 1994 and 2025 with a complete weekly record. The diesel price history chart tables every region's annual average back to 1994.

Monday Diesel reports the West Coast prices and spreads as EIA surveys them and attributes the fuel rules to the agencies that set them. It describes why the region runs high; it does not take a position on the policy or forecast where the gap goes.

Monday Diesel is a free weekly read of the DOE diesel number and what it does per mile. Built entirely from EIA's public data, in your inbox before dispatch, one email a week.