This is a discussion on Anyone use Costco gas station to fill up your vehicle, Grom within the Grom Talk forums, part of the Honda Grom Forums category; Originally Posted by 8701michael I check which pump was last used for premium gas and that's the one I use. From what i can tell ...
2018 GROM: Modified for reliability longevity gas mileage... and fun.
I check for Top-Tier compliance, if it meets that standard, it's good enough for all of my vehicles.
The only stations I have come across that are NOT Top-Tier are
Sam's Club (Walmart's warehouse-club answer to Costco)
BJ's, which is another regional warehouse club.
Because of marketing non-sense (the greatest of which is calling 91 Octane fuel "Premium"), it can be very difficult to determine what difference there really is between brands and locations.
One of the other confounders is that independently-operated stations are more likely to neglect their equipment, which in extreme cases can lead to contamination of the fuel, usually with water or sediment. In most places the facilities are inspected and audited regularly by local government to avoid these issues, but the rigor and frequency of those inspections varies by location.
NBC News: Watered Down Gas is Way More Common Than You Think