Amazon.com (NASDAQ:AMZN) and Costco (NASDAQ:COST) have each managed to boost annual merchandise sales by over $20 billion since 2010. Fool contributor Demitrios Kalogeropoulos discusses how they achieved that impressive feat, and what lies ahead for these two dominating retailers.

Fool contributor Demitrios Kalogeropoulos owns shares of Costco Wholesale. Erin Miller has no position in any stocks mentioned. The Motley Fool recommends Amazon.com and Costco Wholesale. The Motley Fool owns shares of Amazon.com and Costco Wholesale. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.