91 Or 93: What Octane Is Costco Premium Gas?

In the decades since its founding, Costco has become, arguably, the biggest wholesale outlet chain in the world. At this point in the wholesaler's history, the list of things you can't buy inside a Costco store is probably shorter than the things you can, including brand-name televisions. For many years now, that latter list has also included gasoline, with Costco becoming one of the legit go-to spots for Costco members to gas up on the go.

Those members can, of course, expect a lower price at the pump than most other local gas stations. At present, that discount can primarily be applied to three different styles of gasoline: diesel, regular, and premium. While diesel continues to be a popular choice for big rigs and certain cars, trucks, and SUVs, it's safe to assume that most Costco customers are utilizing either regular or premium gas when they pull up to the pump. And for some, the choice between them comes down to each fuel's Octane rating.

While Costco notes that Octane ratings vary by state, regular gasoline is rated at 87 Octane in most areas. Premium gas, on the other hand, generally ranges between 91 and 93 Octane. For Costco gas, premium gasoline is typically rated at 91 Octane. That rating is, in fact, the only difference between regular and premium gasoline. And it matters because Octane controls the rate at which fuel burns in your engine, which may impact the operation of high-performance vehicles in particular.    

With the Octane questions covered, there are a few other things you might want to know about Costco's fuel operation. First and foremost, you might be wondering who, exactly, can purchase Costco's gas. At present, that honor is reserved solely for consumers with an active Costco membership. There is, however, one exception to that rule, as folks with a valid Costco Shop Card — in-house gift cards that can be used by anyone, including non-members — can also fuel up at the wholesaler's gas stations.

As for how Costco knows whether or not you're a member, you are required to swipe your card at the pump before fuel can be discharged. While all Costco gasoline contains Ethanol as required by the United States government, the wholesaler's diesel fuel only contains biodiesel elements where it's required by law. The company has also recently dipped a toe into the renewable biomass-based diesel market, offering the eco-friendly fuel at certain locations. It should be noted, however, that the availability of that fuel is largely restricted to Costco gas stations in California.

If you're interested in Costco's at-the-pump savings, you should know that you can save a little more by signing up for Citibank's Costco Anywhere Visa Card. That card provides users with 5% cash back on all purchases at a Costco gas station on a per year spend of $7,000, after which point the rewards dip to 1%. Just for the record, that card also delivers 2% cash back on all other Costco and Costco.com purchases, as well as rewards from various other consumer outlets.