Amazon is now the most-valuable retail brand in the world, according to Millward Brown's 2011 BrandZ study of the most-valuable global brands. Amazon edged out Walmart to attain this feat.

Amazon edged out Walmart as the most-valuable retail brand by Millward Brown's accounting, with its brand value rising 37% to $37.6 billion as Walmart's fell 5% to $37.3 billion. Walmart parent Wal-Mart Stores still has more than 10 times the sales and more than five times the market capitalization of Amazon. But BrandZ's calculation subtracts tangible assets from market value to help estimate brand value. Amazon, with no physical stores, fares well in that process. The Walmart brand value also doesn't include Sam's Club or other overseas affiliates with different brand names owned by Wal-Mart Stores.

Even so, Amazon's rise, combined with declines in brand value not only for Walmart but also for other top global retailers Tesco and Carrefour last year, marks the shift toward e-commerce.

"Amazon benefits incredibly by having user reviews integrated into its site," said Eileen Campbell, global CEO of Millward Brown. "Everybody does that now, but Amazon was the first, so it's done an incredibly good job of building trust."