E-commerce sales via the Amazon.com Inc. marketplace increased 27% year over year in January for clients of ChannelAdvisor Corp., far exceeding the 6.8% growth rate for sales via eBay Inc.

ChannelAdvisor produces monthly reports that compare its merchant clients’ sales through various online marketplaces and marketing channels, including Amazon.com, eBay Inc. and Google Shopping. The report comes as the e-commerce service provider reports a 25% revenue gain for 2014.

The Amazon growth rate for January compares with the Amazon growth rate of 21.8% for December. EBay’s December 2014 same-store sales growth rate was 5.8%. The growth rate for other online marketplaces stands at 27.2% for January, down from 28.5% for December.

Sales through eBay auctions decreased 16.2% year over year in January compared with a 12.9% decrease in December. EBay fixed-priced sales increased 7.3% in January compared with a 5.7% increase in December, ChannelAdvisor says. Sales via eBay Motors—that is, auto parts and accessories sold by ChannelAdvisor retailer clients—increased 13.4% in January compared to 12.6% growth in December.

As for Amazon, ChannelAdvisor reports that its clients fulfilled 39.6% of their gross merchandise volume processed through Amazon by that e-retailer’s Fulfillment by Amazon program, which enables retailers to hand off fulfillment tasks to the No. 1 e-retailer in the Internet Retailer 2014 Top 500 Guide. That rate compares favorably with the 32% posted in January 2014 but falls well short of the 56% “high-water mark” recorded in November 2014.

Additionally, the January same-store sales for ChannelAdvisor clients selling through comparison shopping engines decreased 9.4% year over year compared with a 2.3% decrease for December. “This was largely driven by weakness in the traditional CSE segment that overshadowed strength in Google Shopping/PLA,” the report says, referring to Google’s comparison shopping effort and its Product Listing Ads. Those are paid image-heavy marketing messages that appear toward the top of search results pages. Google Shopping sales increased 10.1% year over year in January compared with a 13.2% increase for December.