eMarketer predicts that online retailers in the US will ring up over $100 billion more in sales in 2012 than they did in 2007.

Sales growth will come mainly from consumers who are shifting their spending from traditional retail stores to the Internet.

At least two other research companies have projected retail e-commerce sales through 2012.

eMarketer's numbers lie closest to those from JupiterResearch, which predicts $215 billion in retail e-commerce sales in 2012.

Forrester Research's projections put US retail e-commerce sales at $334.7 billion in 2012.

A large part of the difference lies in what categories are covered in each forecast. Forrester includes event tickets and digital download sales, while eMarketer considers those to be services.

Forrester also attributes higher gross merchandise sales to online auctions than eMarketer.

eMarketer forecasts a 12.0% online sales average annual growth rate from 2007 to 2012. This is higher than Jupiter's 10.9% forecast, but lower than Forrester's 13.8% growth rate.

Among other firms which estimate future US retail e-commerce sales, JP Morgan was one of the more aggressive. The investment bank made projections through 2010, when it said that online merchants would bring in $245.5 billion.

Despite forecasts of e-commerce annual sales growth rates dropping into the teens in 2007, online sales growth rates far outpace retail industry sales growth rates of mid-to-low single digits. Slower e-commerce sales growth is the inevitable result of a maturing sales channel sales, not a sign of consumer disenchantment with online shopping.

The eMarketer Multi-Channel Retailing report will be published this month. Click here to be notified when it is released.