Many of the leading online retailers are reaping the rewards of mobile commerce. The top 366 U.S. retailers will hit mobile commerce sales of $59 billion this year, an increase of 74% from $34 billion a year ago, according to a new index. The world's 500 largest mobile commerce businesses combined will increase their mobile sales by 80% to more than $84 billion this year, according to the Internet Retailer index, which ranks the 500 leading Web merchants globally and analyzes their mobile commerce activity. The index comprises an analysis of 53 data elements, such as mobile traffic, site speed on smartphones, mobile conversion rate and a breakdown of sales between smartphones and tablets. The index lists 134 overseas retailers in the top 500 with a forecast of them reaching $25 billion in mobile commerce sales this year. This would be an increase of 96% from a year ago. Of the 500 leading retailers in mobile commerce globally, most are in the U.S. and U.K. Here are the leading countries with the number of merchants in the top 500: