RESTON, VA: Ecommerce continues to boom in the US, with holiday season online spending up 12% from 2009 as retailers offer discounts, promotions and free shipping in a bid to lure more customers.

According to a new report from comScore, American consumers spent just over $17.5bn (€13.2bn, £11bn) online from November 1st to December 5th, with seasonal free shipping offers from e-tailers helping to boost growth.

With ecommerce giants Amazon and Walmart both offering free deliveries for many sales during the festive season, the proportion of overall transactions with free shipping has exceeded 50% for three of the past five weeks.

This has boosted sales, as the typical free shipping transaction has a basket value 30% higher than those without.

Gian Fulgoni, comScore chairman, said: "Without a doubt, free shipping has become a critical driver of ecommerce purchasing, with the majority of consumers indicating that they will abandon their shopping carts if they get to check-out and find that free shipping is not included."

The impact of Cyber Monday, which fell on November 29th this year, has also been a crucial factor in this year's higher sales.

ComScore said it had delivered a sales record, with the $1.03bn spent during the day 16% higher than Cyber Monday 2009, the previous busiest ecommerce day on record.

A total of $407m was also spent on Thanksgiving day (November 25th), 28% up on last year.

But over the days following Cyber Monday, growth rates "subsided", with the week ending December 5th seeing a year-on-year increase of just 9%.

"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," Fulgoni added.

Amanda Yates of Interbrand also noted that many US retailers have concentrated on online promotions this year, with some even discounting goods prior to Black Friday - traditionally the biggest in-store festive sales day, which fell this year on November 26th.

"With these deals available, along with the added convenience of product reviews, price comparisons, larger inventories, and in many cases free shipping, it's no wonder more and more shoppers are choosing the ease of online shopping," she added.

"The so-called Cyber Monday is actually a Cyber Season."

Data sourced from comScore/Interbrand; additional content by Warc staff