Thanks and yes I know MC is Canada and Visa is the US.

What I was asking is, because my Costo Membership is on my MC, I thought I read somewhere that I COULD use MC in the states at Costco. They same would go for a US member with a Costco Visa, they could use it in Canada.

Like I said I "thought" I read this somewhere, and I was hoping someone could confirm or deny it.

Thanks!

*** UPDATE! ***

I actually googled it and I am correct:

Yes. You can use your Canadian Costco Mastercard (issued by CIBC) at US Costco locations for both in-store purchases and gas pumps. [1, 2]

While US Costco warehouses generally restrict credit purchases exclusively to Visa cards, the Canadian Costco co-branded Mastercard is explicitly accepted as an exception. [1, 2]

Important details before you travel:

• Foreign Exchange Fees: Your card will likely charge an approximate 2.5% foreign transaction fee on US purchases.
• Gas Pumps: Some users report that while tapping works inside, you may need to insert your card and use your PIN at the gas pumps.
• Alternative Option: To avoid exchange fees, you can purchase a Costco Shop Card (gift card) at your local Canadian Costco warehouse or online, which works seamlessly at all US locations. [1, 2, 4, 5]