Mobile commerce continues to gain momentum as a mainstream way for consumers to shop online. In fact mobile commerce now accounts for nearly one-third of all U.S. e-commerce sales, according to an analysis of data from Internet Retailer’s newly published 2016 Mobile 500.

In 2015 U.S. mobile commerce sales will total $104.05 billion, up 38.7% from $75.03 billion in 2014, reveals data from the 2016 Mobile 500. Internet Retailer estimates that mobile commerce in 2015 will grow 2.58 times faster than total e-commerce sales, which Internet Retailer projects will grow 15% this year to an estimated $350.64 billion.

But mobile commerce in the U.S. isn’t growing nearly as fast as in other global regions. The combined sales of the 14 Asian retailers ranked in the 2016 Mobile 500 grew year over year 249.3 %, or 6.4 times faster than 378 ranked U.S. Mobile 500 merchants. In 2015 the 93 European Mobile 500 merchants also will grow their collective mobile sales, by 70.7% or 1.82 times faster than their U.S. counterparts, while the seven Latin American Mobile 500 retailers increased their total mobile commerce sales 59.6% or 1.54 times faster than the U.S. retailers.

In the U.S. mobile commerce is becoming a bigger part of e-commerce overall.

In 2015 Internet Retailer projects that mobile commerce will account for about 29.7% of all U.S. e-commerce sales compared with 24.6% in 2014. There are other statistics confirming that more consumers are using web-enabled smartphones and tablets in general. Web measurement firm comScore Inc. estimates 189.7 million consumers, or nearly 60% of the U.S. population of 319.8 million, now own a smartphone. And U.S. consumers are using those web-connected more often to shop on U.S. mobile sites and through mobile apps.

The combined monthly mobile visits of all 378 U.S. Mobile 500 merchants grew 68.3% to 3.03 billion in 2015 while mobile monthly unique visitors grew collectively 44% to 964.7 million. The increase in mobile shopping is leading more U.S. retailers to invest in mobile apps, which can provide features not available on a mobile web site. 180 U.S. merchants in the 2016 Mobile 500 have one or more apps, and the combined sales from those apps increased 44% to $40.58 billion in 2015.

RealTruck.com, No. 295 in the 2016 Mobile 500, is an example of a U.S. retailer that’s registering mobile sales growth after making it a priority to cater to mobile shoppers. The retailer’s mobile sales are projected to grow by 107% and reach $18.0 million in 2015,.

RealTruck.com doesn’t have an app but its mobile site has been updated and streamlined over time to let web shoppers search and purchase parts and accessories by vehicle make, model year and by popular category. Other categories also get shoppers to products organized alphabetically by product category or by best-seller.

“A focus on mobile and catering to our mobile shoppers has been a 2015 strategic initiative for RealTruck.com,” says marketing manager Antinea Ascione.”We have been ensuring that we design specifically for mobile when possible, and keep mobile in mind with every project we implement.”