Online retail in the U.S. and Western Europe will continue to have double-digit growth over the next five years, according to a new report from Forrester Research.

U.S. and European online retail will grow at a 10 percent compound annual growth rate (CAGR) from 2010 to 2015, reaching $279 billion and €134 billion, respectively, in 2015. The forecasts include business-to-consumer sales excluding travel and financial services.

“The online retail market in both the US and Western Europe remains strong, despite the challenging economy,” said Forrester Vice President and Research Director Patti Freeman Evans.

“In fact, with consumer purchasing behavior returning to normal, US web sales in 2010 actually accelerated over 2009 compared with the prior year, growing 12.6 percent. In Europe, very strong growth in 2010 was fueled by new online buyers and higher spend per capita on the demand side, as well as the launch of transactional websites by established offline players.”

Retailers are supporting consumers’ increasing use of the Web in the US, helping to drive growth with new business models, such as flash sales and group buying, as well as improved merchandising to provide a broad selection of products available online.

In Western Europe, the online retail market grew 18 percent from 2009 to 2010 and is projected to grow 13 percent from 2010 to 2011, but growth rates will then slow as the market matures and buyer penetration begins to level off. By 2015, 68 percent of online adults will have made a purchase online; however, northern European countries will see 80 percent or more of their online population buying on the web, versus less than 50 percent in southern countries.