Online shoppers didn't wait around until Cyber Monday to start their holiday shopping.
According to IBM Corp. research unit Coremetrics, U.S. consumers spent 20 percent more online on Black Friday, the day after Thanksgiving, this year than last, while online sales jumped 39 percent on Thanksgiving Day.
Coremetrics measures sales data from more than 500 online retailers, including half of the top 50. It doesn't reveal its partners or specific dollar figures.
Both Coremetrics and e-commerce payment site PayPal, a united of eBay Inc., said shopping by mobile phone is increasingly substantially this year. PayPal said it saw five times more mobile payments worldwide this Thanksgiving, compared with last year.
And Coremetrics said about 17 percent of Black Friday visitors to retail websites came via mobile devices, up from about 5 percent a year ago.
There were sporadic reports of shoppers having trouble with crowded websites. Some visitors to Walmart.com reported problems paying for their merchandise at checkout, according to posts on GottaDeal.com and other websites.
Toys R Us Inc. spokeswoman Kathleen Waugh said Friday that the toy retailer's site experienced "some slowness" when it unveiled some online deals at 9 p.m. Eastern time Thursday. She said the company's online sales are up "extensively" from a year ago.
Online sales typically account for about one-tenth of total sales in November, one of the biggest shopping periods of the year, said John Squire, an executive with IBM's e-commerce marketing unit.
That share looks to rise this year.
IBM's Coremetrics predicts online sales will grow about 15 percent this year, compared with growth of a few percentage points for brick-and-mortar stores.
Some retailers save their online deals for the first business day of the week following Thanksgiving, now known as Cyber Monday. And Squire predicted that Cyber Monday's online sales will exceed the total reached on Black Friday by early afternoon.
Squire said its partners' websites hadn't had major glitches Thursday or Friday.
"People keep spending money online, so that's a great indicator that the sites are running," he said.