Costco gasoline is appropriate for an Audi when you buy the octane the owner’s manual requires. U.S. Costco fuel is TOP TIER detergent gasoline, a standard several European makes recommend to keep injectors and valves cleaner than the federal minimum.
Octane first
Many Audi gasoline engines specify premium. Costco premium is often 91 AKI and sometimes 93 — see 91 or 93. If the manual requires 91 or higher, do not substitute Costco 87 regular. If the manual allows 87, Costco regular is the cheaper TOP TIER option.
What Costco is not
It is not ethanol-free (typically E10) and it is not Techron. Neither fact bars Audi use if the car is rated for E10, which modern Audis are. More: ethanol, Techron.
Find a warehouse from U.S. Costco gas prices or a metro page such as Los Angeles.