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Among the more basic problems for merchants, Mr. Brewer said, is simply avoiding duplicate numbers on the certificates. Some big retailers generate tens of millions of gift cards and online gift certificates each year, with individual stores often tracking their own card inventories.

Stored Value coordinates such tasks for retailers, puts antifraud measures in place and installs hardware for reading the cards, Mr. Brewer said, at a cost he would not disclose. As a testament to the growth in this area, Mr. Brewer said revenues at Stored Value Systems doubled in 2001, to $46 million, and would show substantial growth again this year.

Some retailers choose to build and manage their own gift certificate technology for modest sums.

Sharper Image invested less than $100,000 three years ago on such a system. Since then the returns have been solid, according to Tracy Wan, the company's president.

Amid a "phenomenal" selling season, she said, Sharper Image "saw a nice uptick in online gift certificate sales."

Notably, about half of the company's gift certificate sales come from GiftCertificates .com, which sells certificates for about 300 merchants. Ms. Wan said GiftCertificates .com had done a good job of marketing itself through search engines and the like over the last few years, generating more business.

GiftCertificates.com has thrived as well, reaching a positive cash flow in its fifth year of operation. Michael Ahern, the chief executive, said GiftCertificates.com was on track to reach $75 million in revenue this year — 30 percent more than last year — thanks largely to a record holiday season. GiftCertificates acts as a wholesaler, Mr. Ahern said, buying certificates at a discount of roughly 16 percent before selling them at face value.

The most popular product on the Web site is the SuperCertificate, a gift card that can be redeemed at various retailers, but Mr. Ahern said e-mail gift certificates accounted for 40 percent of his business, a share that is growing quickly. Not only are consumers more comfortable with the notion of virtual gift certificates, he said, but many merchants are only now starting to update their technology to offer such a service, in part to stretch their online sales season a few more days.

That is not to say that ordinary mail does not have its place. Mr. Ahern said the company had mused about offering a service for customers who were late with a gift. "For $15 or so, we could put a gift certificate in a really beat-up envelope with a message saying, `Sorry, it's our fault it showed up late!' " Mr. Ahern said. Though the company has so far thought better of the move, he said, "maybe we'll get it running for Valentine's Day."