Driven by a strong rise in holiday spending, U.S. retail Web sites crossed the $100 billion mark for the first time, collecting $102.1 billion in 2006, a 24 percent increase over the previous year.

Holiday shoppers spent $24.6 billion in the last two months of 2006, representing a rise of 26 percent over the same period in 2005 comScore Networks said on Thursday.

2006 was certainly an exceptional year for online retailers as e-commerce spending eclipsed $100 billion for the first time, and growth remained very strong with a 24-percent increase versus last year, said Gian Fulgoni, chairman of comScore.

The online holiday shopping season of course played a vital role in the year’s success, as spending accelerated during the final two months of the year.

The top three days of online spending for the year were Dec. 13 ($666.9 million), Dec. 11 ($660.8 million) and Dec. 4 ($647.5 million).

The numbers include consumer spending in all sectors except travel.