comScore (NASDAQ:SCOR) said online holiday spending in the United States exceeded $17.5 billion for the first 35 days of the November-December shopping season, up 12 percent from last year.

The report from comScore said free shipping surged to more than 50 percent of all the E-Commerce transactions. The week ending Sunday, November 28 showed a peak free shipping rate of 55.1 percent, 9.6 percentage points higher than the year-ago levels.

Retailers have increasingly responded to this consumer demand, with market leaders Amazon and Walmart both offering free shipping on virtually all transactions this season, comScore said.

According to comScore, Cyber Monday became the heaviest online spending day on record at $1.028 billion, up 16 percent. During Thanksgiving day, spending grew 28 percent to $407 million.

We anticipated that the post-Cyber Monday period would experience a slight hangover after many of the retailers’ most aggressive deals and promotions expired, but we can expect to see activity begin to pick up again next week as we get into the middle part of December when online buying typically peaks, said comScore chairman Gian Fulgoni.

For the week ended Dec. 5, spending rose 9 percent to $5 billion.