Online retail sales this holiday season—Nov. 1-Dec. 24—totaled $27.12 billion, a 4.9% increase compared to $25.85 billion a year ago, reports web measurement firm comScore Inc. From the day after Thanksgiving to Christmas Eve alone sales grew by approximately 3.5% (after adjusting for the additional shopping day this year).

More people buying online helped offset a slight decrease in the amount spent per buyer, says comScore chairman Gian Fulgoni.

“The season featured a strong start as a result of early retailer promotions and a very strong finish helped by the snow storms that occurred the weekend of Dec. 19-20, retailers’ willingness to offer free shipping later in the season, and consumers’ confidence in expedited shipping arriving in time,” says Fulgoni. “This was also a year when retailers substantially boosted their use of social network marketing and the larger retailers significantly outperformed their smaller brethren. In these tough economic times, the retailers with sufficient financial resources and a willingness to invest in aggressive marketing and free shipping offers were clear winners.”

The strong finish to the holiday season was helped by the heaviest online spending day in history—Tuesday, Dec. 15, with $913 million—as well as the huge snowstorm that blanketed must of the eastern portion of the nation last weekend when sales shot up 13% compared to the final weekend before Christmas last year.