Looking to give your company’s digital retail sales a boost? Then it may be high time you turned some attention to the tablet. 

A whopping 79.4 million U.S. consumers—51 percent of all digital buyers—will use a mobile device for online purchases in 2013, according to new estimates from eMarketer. That traffic will constitute 15 percent of all ecommerce retail sales, up from 11 percent in 2012, and will spur $39 billion in sales.

And among digital buyers, tablet users are going to make the most noise.

Having a tablet “almost guarantees that the person uses it for ecommerce,” the report said. By 2017, 78 percent of U.S. tablet users will make purchases via the device, making up nearly 72 percent of all U.S. retail ecommerce sales. By comparison, 59.9 percent of buyers will be in the smartphone camp, with their dollars accounting for 27 percent of sales.

While some mobile sales merely reflect a transfer of purchases that would otherwise happen on a PC or laptop, mobile devices also stimulate purchases in other ways. The report explained:

Mobile is an ecommerce sales driver in two ways: It gives consumers reasons to shift spending from stores to the Internet, and it stimulates incremental purchases that stem from impulse buying. Smartphones and tablets promote ecommerce by extending the shopping day and untethering consumers from the desktop or the store.

These estimates are down slightly from eMarketer predictions released in January 2013, which pegged 2013 mobile commerce sales at $38.4 billion.