Ben Margot, Associated Press Workers use forklifts to move boxes with merchandise Tuesday at the Amazon.com fulfillment center in Fernley, Nevada. The facility, with more than 800,000 square feet, or roughly 13 football fields, is capable of handling hundreds of thousands of orders per day. Click photo for larger image. Related article Hot toys getting scarce on retailers' shelves

At 2:30 p.m. Tuesday, shoppers who went to NittanyOutlet.com for Penn State gear to give to loved ones and friends could still place Christmas orders. By 5 p.m., a red box appeared on the site warning holiday shoppers anything ordered after 3 p.m. that day was not likely to arrive before Dec. 24.

The online holiday shopping season is at its peak, with analysts predicting the busiest Internet sales day could have come this past Monday, or maybe Tuesday -- or may not come until next Monday. Truth is, no one knows for sure. A lot depends on how many retailers can make promises of prompt shipping to make sure that special package arrives before Dec. 25.

Whatever the busiest day, it's clear that while the overall gift-giving season has produced mixed sales results so far, Internet shopping is surging. It's up 23 percent over last year, according to comScore Networks, the Reston, Va.-based consumer research firm. It estimated that $12.75 billion of non-travel consumer spending took place online between Nov. 1. and Dec. 9.

Trying to capture whatever last-minute rush comes, online stores are stepping up promotions and pushing shipping deadlines.

Sears yesterday sent out an e-mail advertisement headlined, "Big ideas for when little time is left," noting free shipping ends after Sunday. Best Buy ran a two-day online sale yesterday and today, just under a reminder to order by Monday. Wal-Mart alerted the media yesterday to the important news that it is there for the procrastinators, but that its cutoff for standard shipping rates does happen to be tomorrow.

And Amazon.com's Web site is counting down the last Free Super Saver Shipping day, which ends tomorrow to be sure of Dec. 23 delivery. A company spokesman noted that doesn't mean shoppers can't still make it work. They just have to be willing to pay more.

Trying to stand out in the crowd, online jeweler Blue Nile is promising Christmas Eve delivery on orders placed by 3 p.m. Dec. 23, including free shipping for those priced above $100. Jewelry tends to be easier to move quickly than, say, appliances and 36-inch TVs, which Best Buy warns should be ordered by today to be assured of Dec. 24 arrival.

When the final tally showing which day most online shoppers hit the keyboard comes, Carnegie Mellon University associate professor of marketing Ajay Kalra expects it will turn out to have been on a Monday, most likely the one just passed. He believes many people want to check out a product in person, likely over a weekend, before they return to look for the best deals online.

In the future, he said, the busiest online shopping days may come later in the season as more retailers allow customers to order online and then pick up the items in stores, something both Circuit City and Best Buy are pushing.

As for the biggest shipping day, FedEx Corp., the company that owns Moon-based FedEx Ground, was projecting this past Monday would bring about 8.5 million packages, or 400,000 more than last year's peak. Company spokeswoman Allison Sobczak said FedEx hit its projections. "It was a very good day, a very busy day," she said.

FedEx handles shipping both for the merchants selling goods and consumers receiving them, so its peak might not coincide exactly with timing of shoppers sitting down at their computers.

High gas prices, which were expected to be a boost to online shopping, seem to be having a mixed impact.

A survey released yesterday by The Conference Board and research firm TNS found consumers earning less than $35,000 and those between ages 35 and 54 would be most affected by rising energy costs. More than 22 percent of the "modest earners" planned to shop online to save on energy costs, according to the fourth-quarter survey of 10,000 households. The survey found more affluent households also shopping more online.

Dr. Kalra believes consumers have been more focused in recent weeks on how far gas prices have fallen from earlier this year, even if they remain high. Still, he said online retail is having a big year and it may hold onto the gains in the future no matter what energy prices do.

Nielsen//NetRatings reported that last week alone, online shopping visits rose 33 percent from 348.3 million last year to 462.5 million this year. The books-music-video category was especially strong, followed by apparel and toys.

At mid-day yesterday, Amazon's Web site indicated more than 90 million items had been ordered since Nov. 1. Just five years ago, the company had just under 40 million items ordered during the entire holiday season.

To be sure, online retail remains just a slice of total holiday shopping spending, which the National Retail Federation projects will be more than $400 billion this year. And on the traditional front, the retail industry is heading into its final big rush.

Last year, the biggest bricks-and-mortar shopping day was the Saturday before Christmas, Dec. 18. This year, the picture is muddied for retailers trying to time promotions because Christmas comes on a Sunday and Hanukkah starts the same day. Shoppers may try to get done this weekend or leave some things until Christmas Eve.

It does seem that consumers seem to be taking the usual wait-and-see attitude as they seek out good prices. By last Sunday, only 13 percent of households were done with their shopping, according to the International Council of Shopping Centers. That's the same number as last year.