Brick-and-mortar retailers should expect no relief from Amazon.com’s relentless march to e-commerce dominance. The online retailer, which accounts for about 34% of U.S. online sales, should see that market share grow to about 50% by 2021, helped how the popularity of its Prime membership program and its marketplaces, Wall Street firm Needham said in a research note on Monday. The firm upgraded its rating on the stock to buy from hold and set a price target of $1,100 on the already soaring shares. “We believe Amazon’s established dominance in the U.S. is sustainable with Prime, mobile penetration and third-party growth,” Needham analyst Kerry Rice wrote in the note. While traditional retailers are enjoying strong online growth- Kohl’s, J.C. Penney and Target enjoyed record internet sales during the holidays, Amazon is still outpacing the overall industry’s growth, extending its lead over rivals. Walmart has made large strides in the last year thanks to an overhaul of its third-party sellers and its purchase of jet.com, but its sales remain a fraction of Amazon’s. Amazon’s not-so-secret weapon is Prime, which offers subscribers free two-day shipping for a $99/year fee, along with entertainment like television shows and streaming music. Research firm Consumer Intelligence Research Partners estimates Amazon had some 65 million Prime members last year, more than double the number two years earlier. And those shoppers are more active and loyal as they try to make the most of the investment: Needham cited data from eMarketer that found 80% of Prime members shopped on amazon.com at least once a month. CIRP found Prime members spend up to $1,500 a year on the site, more than twice non-members. Read more at Fortune.