U.S. online sales in the holiday season to date are up 15 percent to $24.6 billion, according to comScore.
The research firm said Sunday sales on six individual days during the first 39 days of the November-to-December shopping season have exceeded $1 billion, led by Cyber Monday, the Monday after Thanksgiving, when sales hit $1.25 billion.
Sales in the most recent week ended Dec. 9 rose 15 percent to $5.9 billion, the Reston, Va., company said.
"As we enter what will be the heaviest week of the season for online retailers - beginning with `Green Monday' on Dec. 12 - all signs are now pointing to a strong finish to the season," comScore Chairman Gian Fulgoni said.
Over the past six years, "Green Monday" - a term coined by eBay Inc. and traditionally the second Monday of December - has consistently ranked among the top spending days of the season, although it is no longer the top online spending day.
According to a representative from ecoupons.com, online retailers expect more than a billion dollars in sales on "Green Monday." They also say it is the busiest day in Fedex history with more than 17 million shipments wordlwide.
Fulgoni said a possible reason for that change is the emergence of "Free Shipping Day," which occurs on Friday, Dec. 16 this year. "Online spending during the heaviest week of the season is being more evenly distributed throughout the week, whereas in the past there was a much higher concentration of spending during the early part of the week."