Not every Costco gas station sells diesel. Warehouses that do will list a diesel price on this site when we have a reading; stations without diesel simply have no diesel product, not a “hidden” pump.
When diesel is offered, it is still members-only and subject to the same hours as that warehouse’s fuel island. Ultra-low sulfur diesel (ULSD) is the U.S. on-road standard; do not assume off-road or dyed diesel at Costco.
How to check a warehouse
Open the station page from a state or city list — for example United States, California, or Ottawa — and look at the diesel row. “Not reported” means we do not have a price, not that diesel is confirmed. Costco’s warehouse locator is the backup if you need the pump confirmed today.
Gasoline grades and additives are separate from diesel. For unleaded quality, start with additives and premium octane.