comScore estimates U.S. PC e-commerce sales rose 13% Y/Y in Q3 to $47.5B. That's down from Q2's 16% clip, and matches Q1 2013 for the slowest pace seen in the last two years.
But the firm also believes U.S. mobile e-commerce sales rose 26% to $5.8B. That's a pickup from Q2's 24% clip, and gives mobile an 11% share of total U.S. e-commerce spend. comScore thinks mobile sales will be near $9B (+25% Y/Y) in seasonally strong Q4, and have "an outside shot of hitting $10 billion." 62% of Q3 mobile spending is believed to have come from smartphones, and 38% from tablets.
Recent industry commentary has been mixed. eBay (EBAY -0.4%) provided light Q4 guidance while stating U.S. e-commerce growth was slowing, but the company partly backtracked on its comments. Groupon (GRPN -2.8%) partly blamed its Q3 revenue miss on seasonal weakness, but is optimistic about holiday season demand. Amazon (AMZN +0.7%), which has been gaining U.S. e-commerce share for some time (Q3 North American sales +31% Y/Y), has been fairly upbeat.