Large online retailers are seeing a big jump in their sales — more than 15 percent — so far this holiday season, according to data collected by Chase Paymentech, a big Internet payment processor, which claims to have handled more than 50 percent of Internet transactions in 2008. The data that’s collected as Chase Paymentech’s Pulse Index, which measures same-store sales growth at large online retailers, was published by J.P. Morgan equity research group in a note to its clients this morning. Here are some more stats:

• There’s been $7.38 billion in total online sales since early November to December 16 vs. $6.40 billion during the same period in 2008.
• That’s a 15.3 percent gain.
• The good news is that the number of online transactions has increased by 25 percent, so people are getting used to buying online.
• The bad news is that average selling prices sizes are down to $55 in 2009 vs. $59 a year ago, a decline of 8 percent.

In a press release last month, the company shared some other interesting stats: For the first five shopping days following Thanksgiving, online transactions were up 32 percent, and sales were up 24 percent. For the full season, transactions are up 25.3 percent.

In case you so desire, check out the Chase Paymentech Pulse Index for more up-to-the minute stats.