With sales of $51.5 billion in 2004, the Top 400 online retailers represent 58 percent of all online sales, according to Kurt Peters, editor of Internet Retailer, and the top 100 account for 53.1 percent of the market, he said, reporting data from the publication's updated rankings of the largest retail websites. He said "after only 10 years, the online market is rapidly approaching the concentration level of offline," where among chain retailers the top 100 account for 63 percent of all sales.

The top 400 combined get 1.1 billion visits a month and together shipped 401.5 million orders in 2004. The top selling categories online were computers and electronics retailers, accounting for 28 percent of all online sales; mass merchants, 27 percent; then office supplies retailers at 12.5 percent ;and apparel and accessories retailers at 9.2 percent.

Chains/stores account for 38.9 percent of sales; web-only merchants, 27.2 percent; consumer brand manufacturers, 18.8 percent; and catalog/call center merchants, 15.2 percent.