The most recent week (week ending Dec. 12) reached $5.31 billion in spending, an increase of 12 percent over the corresponding week last year. Monday, December 13, known as “Green Monday” (the second Monday in December when online spending has historically tended to peak), reached $954 million in spending, representing a 12-percent increase compared to last year.

“Green Monday represented another banner day for the 2010 holiday season with $954 million in spending, ranking as the second heaviest online spending day on record behind this year’s Cyber Monday,” said comScore chairman Gian Fulgoni.

“Green Monday kicks off what we expect will be the heaviest online shopping week of the season right up through ‘Free Shipping Day’ on Friday, December 17. In the past, Green Monday was more reliably the heaviest day of the season, but in recent years we have seen heavy spending days occur even later into the season as consumers continue to gain confidence in retailers and shippers being able to deliver their gifts in time for Christmas.”

As part of the comScore Holiday Shopping Survey, more than 500 people were asked about their holiday shopping for the season so far. More than one-third (35%) said they has already purchased everything they needed this season.

Among the 65 percent who had not finished shopping, 33 percent said it was because of a lack of money available to buy the gifts they wanted. Thirty-two percent said they had not had enough time to finish shopping, while 11 percent were waiting for better deals and 6 percent said they liked last-minute shopping.

“The reasons consumers give for not having finished their holiday shopping reveal some very important dynamics driving the retail industry today,” added Mr. Fulgoni.

“The first is that we are offered a stark reminder that many consumers are still strapped for cash and may be waiting for their mid-December paychecks before they can finish their shopping. The second important point is that it’s clear consumers have significant time constraints in their lives, which is one of the key drivers behind the continuing shift in retail dollars to the online medium, as the Internet enables people to shop for many gifts quickly and more efficiently, not to mention the cost savings that can be realized through e-commerce.”

It’s not another Yahoo story about the environment or Google putting up solar panels. The ‘Green Monday’ name dreamed up by eBay, PayPal, and Shopping.com reflects economic thoughts, not environmental ones.

The logic goes like this: all the big spending for the holidays happens the second week of December. Black Friday, Cyber Monday, they’re nice and everything, but the credit cards really hit the retail world after those days.

According to analysis firm comScore, there may be truth to that theory. Online US retail spending for December 10th, also known as "this past Monday," reached $881 million, 33 percent up from the same Monday last year.

US non-travel retail spending has topped $20 billion from November 1st through December 11th, comScore said in a statement.

"Consumers are clearly responding positively to the enticing promotions and discounts being offered by retailers this year, and spending is currently on track to meet our forecast of $29.5 billion for the season," said comScore Chairman Gian Fulgoni.

Ina Steiner at AuctionBytes said PayPal data shows the second Monday in December has been the busiest online shopping day of the year since 2001. Shopping.com, an eBay property, saw record activity on December 10th this year.

follow me on Twitter