Yes, Costco accepts American Express on its website. In Canada, Costco.ca takes Amex, Mastercard, and Mastercard-branded debit cards for online orders. In the U.S., Costco.com accepts Visa and American Express. This differs from in-warehouse policies where Canada requires Mastercard and the U.S. requires Visa as the only credit options, but both locations accept Amex cards online. The payment acceptance discrepancy between physical stores and e-commerce stems from different merchant agreements and processing costs. Online transactions often have more flexible payment gateway configurations, allowing retailers to accept cards they don't take in-store. Costco negotiated exclusive in-store agreements with single card networks (Mastercard in Canada since 2014, Visa in the U.S. since 2016) to reduce processing fees on high-volume, low-margin transactions, but their digital checkout systems support broader acceptance. From a web design perspective, clear payment method communication matters for conversion rates. Costco displays accepted payment logos in the footer and at checkout, which reduces cart abandonment from customers discovering their preferred card isn't accepted only at the final step. Sites processing 6-figure monthly transactions should display payment options on product pages or prominently in the header, not just at checkout. When we build e-commerce sites at Ottawa SEO, we configure payment gateways to show real-time accepted methods based on cart contents, shipping destination, and transaction value. A customer in Toronto buying $800 worth of items needs to see immediately whether their Amex with its typical 2-3x points on warehouse clubs will process. Payment method visibility directly impacts average order value because customers adjust cart contents based on which rewards card they can use. For enterprise retailers, the cost of Amex's higher merchant fees (typically 2.3-3.5% versus 1.5-2.5% for Visa/Mastercard) gets offset by higher basket sizes from premium cardholders.