Right after they aired in mid-January, the first four episodes of "24" were released on DVD, along with an exclusive look at the next episode of the hit Fox show.

	Shows such as "24," which stars Kiefer Sutherland as Jack Bauer, are offering selected episodes on DVD before they are seen on TV. Click photo for larger image. Related article Networks want TV to be everywhere

The quick release, months before the full season would land on store shelves, was unique for network television and an example of why TV DVDs are leading the sales growth -- and innovation -- in an otherwise flat DVD market. For a number of reasons, from the growing pains of the 10-year-old DVD industry to the peculiar, personal attachment American consumers have for television series, TV DVDs are exploding.

TV DVD unit sales grew 10 percent in 2006 over the previous year, while sales of movie titles grew just 1 percent, according to Nielsen VideoScan. TV titles accounted for 18 percent of the overall DVD market, up from 8 percent four years earlier.

Making their popularity all the more notable is the fact that TV DVDs cost twice as much as their theatrical cousins, costing on average $41 for a full season to the $17 cost of DVD movies, according to analysts at the NPD Group. Packaged multi-season sets of HBO dramas such as "Deadwood" and "The Wire" go for up to $199.

The biggest individual DVD sellers are still movies, such as last year's No. 1 seller, "Harry Potter and The Goblet of Fire," but TV is where the action is.

"When you see things that have big followings, such as 'Grey's Anatomy' -- a major award-winning television show -- it follows that people want to own it or really want the convenience of watching the whole season all at once," said Judith McCourt, research director of Home Media magazine in Santa Ana, Calif.

Shows long off the air, such as the 1989-1992 sitcom "Anything But Love," live again on DVD. Click photo for larger image.

Viewers "want to do pick up the whole set when it comes out. There's a huge fan loyalty that then breeds people wanting to own the shows."

With 10 years passed since DVDs were first introduced in 1997, some trends are clear for this now mature market. As of 2006, more American homes owned DVD players than VHS, according to Nielsen. But fewer DVDs were released in 2006 than the year before for the first time since 1997, according to DVD Release Report, pointing to a glut in the market.

From the beginning, movie DVDs dominated the market, as studios were able to sell not only new releases but also old titles out of the back catalog, often with bonus features. With that theatrical material thinning, TV networks are stepping in with loads of catalog releases of their own, with everything from "Beauty and the Beast" to "McHale's Navy." They also are releasing new movie-length episodes of canceled shows -- such as "Stargate SG-1, playing out its 10th and final season on the Sci Fi Channel, and "Babylon 5" (1993-99) -- straight to DVD.

About half of TV DVD releases are now from the vaults, said Todd Rowan, senior vice president of marketing for Twentieth Century Fox Home Entertainment.

	Movie-length episodes of canceled shows such as "Babylon 5" are now available on DVD. Click photo for larger image.

"We've definitely taken a page from the theatrical DVD business. You've got a library that's now been on DVD for a while, so [the question is] how to keep it fresh, how to reach out to the fan base that's already said [they] really like the show, and to re-engage them with it.

"You do that by adding special features, new disc content, new packaging, collectible things. ... It's how you grow the business as it matures and still provide consumers with value," Rowan said.

A simple reason why DVD sales of TV series is booming lately is their physical size -- collecting several hours or seasons of a show on VHS tape was not practical for most consumers, but with DVD "it's sexy, it's easy, it's little, you can store it. It speaks to collectibility," McCourt said.

Convenience is another factor. Buying an entire TV season works for the increasing number of time-shifting viewers who are "binge-watchers," said McCourt, who will not watch a show all season, then sit down with the DVD box set to watch them all.

TV DVD marketing has lately bundled these factors -- reaching out to collectors, fans and those who missed previous seasons of shows -- when releasing season packages. Networks release the previous seasons of shows on DVD right before new seasons are broadcast, to capitalize on publicity and momentum for both.

Fox did that with the fifth season of "24," which came out in December. Then a month later, after the two-day season premiere of its first four episodes of season six, it released them on DVD as well. The $15 DVD had a $10 coupon for buying any other full-season DVD of the show.

"Really it's a sampling exercise," Rowan said. "We wanted to give people the opportunity -- who for whatever reason missed one of the two nights of the premiere, or both -- to give them a chance with very little financial cost to experience the show and immerse them in season six, so that they come back and then stay with the show all season, and really establish a relationship with the broadcast.

"We don't want them to write off the show because they missed the beginning."

Many top-rated shows -- including "24" and dramas on HBO and other networks -- are notably complex and well-made, allowing them to stand up to repeated viewings on DVD. Those qualities have been lacking in many of the high-profile mainstream films the past few years, judging from both box-office and movie DVD receipts.

The 2005 box office was notoriously bad -- with Hollywood suffering its worst year in almost two decades -- so when those same movies came out later on DVD, performance wasn't much better. Customer polls by NPD Group, a Port Washington, N.Y., market research firm, show there is lagging interest in upcoming movie DVDs, too.

"Ten years into the DVD life cycle, there's a question about the pipeline that they get from theatrical. A lot of consumers are saying there's content drought," said NPD movie analyst Russ Crupnick. "Candidly, Hollywood has had a mixed couple of years putting things out that people want to own."

If TV DVDs do follow the movie road map, there could be bumps ahead. Consumers switching to high-definition screens are waiting to see which of the two HD DVD formats will win out, said McCourt, and others are switching to online downloads of TV shows and films (although those numbers are still relatively small).

As for leaning on the back catalog, studios face challenges when trying to clear the music rights for soundtrack-heavy shows -- the costs of those rights are blocking Fox from releasing shows such as "Ally McBeal" and "Wonder Years.

Quality, said Rowan, has to continue to feed the TV DVD market.

"But the speed at which the market grows is directly tied to new television releases. ... Quality TV shows are just fantastic, and there's a lot of them."

Of course, even with questionable quality or niche followings, canceled shows get another day in the sun -- Fox is releasing the Richard Lewis-Jamie Lee Curtis sitcom "Anything But Love" (1989-92) today -- the possibilities for the TV on DVD market are limitless.