SAN FRANCISCO, Nov. 1 (Xinhua) -- Online retail spending in the United States reached 32.1 billion U.S. dollars in the third quarter this year, up 9 percent from the year-ago period, market research firm comScore reported on Monday.

According to comScore, it was the fourth consecutive quarter of positive year-over-year growth following a year of flat or negative growth rates.

The top-performing online product categories in the quarter were books and magazines excluding digital downloads, as well as computers and consumer electronics, indicating a higher willingness of consumers to spend on in-home entertainment, comScore noted.

"Retail e-commerce growth in the third quarter remained solid at 9 percent, a fairly positive indicator for the upcoming holiday season," comScore chairman Gian Fulgoni said in a statement.

However, he cautioned that factors such as the continuation of high unemployment may limit consumers' confidence to spend freely.

"Until the economy begins adding jobs at a meaningful rate, the lack of spending power among consumers will continue to be a drag on purchasing, with many consumers indicating their intention to cut back on gift buying this holiday season," Fulgoni said.