On the mainstream-entertainment radar, the CW network’s “Supernatural” is just a blip, a scrappy little TV show that is routinely clobbered in the Thursday-night ratings by “Grey’s Anatomy” and “CSI.”

And when Comic-Con is over, shows such as “Battlestar Galactica” and the canceled “Veronica Mars” will continue to generate a pop-culture buzz through merchandise, their own magazines, more conventions and even the occasional cruise.

In the ever-expanding fan universe, the TV shows that make the most noise are often the ones most viewers have never heard of.

“I think the fact that we are not an out-of-the-box hit actually helps,” said “Supernatural” creator Eric Kripke. “Everyone feels like they’re in on this very, very cool, wonderful thing that the general public doesn’t know about. It makes them feel like insiders, and who doesn’t want to feel that way?”

Comic-Con is sold out, with more than 124,000 people expected to attend. The annual celebration of science fiction and fantasy-inspired entertainment is one of the biggest fan events in the country, and one of the biggest things it celebrates is the concentrated power of the cult TV audience.

On Saturday, “Battlestar Galactica” fans will jam into a 4,500-seat ballroom for an always-riotous panel discussion dedicated to the Sci Fi Channel’s smart space epic. Lines will form hours in advance for Thursday’s panel dedicated to BBC America’s witty (and wiggy) “Torchwood.” Fans will risk life, limb and personal space on Saturday to grab autographs from “Supernatural” stars Jensen Ackles and Jared Padalecki.

With the exception of “Lost” and “Heroes,” sci-fi and fantasy shows require more dedication than mainstream viewers are willing to give. Keeping track of the complex, politically informed theories of “Battlestar Galactica,” the multilayered mythologies of “Stargate Atlantis” or the knotty, demon-plagued family dramas of “Supernatural” takes time, patience and the willingness to watch every episode more than once.

“These fans immerse themselves in the story, and it is that immersion that makes them different,” said Lisa Gregorian, executive vice president of worldwide marketing for the Warner Bros. Television Group.

But in the all-engulfing cult TV world – where sci-fi and fantasy titles accounted for 60 percent of Amazon.com’s 25 top-selling television DVDs, Comic-Con is just the beginning.

“These shows really speak to people on a deeper level,” said Christy Black, a “Firefly” and “Veronica Mars” fan who has organized cruises dedicated to these canceled dramas. “And once you have utilized all there is on the DVDs and you’re still excited about the show, you want more.”

How much more? How about subscriptions to “Smallville” or “Stargate Atlantis/Stargate SG-1” magazines, just $39.95 for six issues a year? Or $47.99 for a “Firefly” hoodie? Or tickets to star-studded conventions dedicated to “Supernatural” or “Battlestar Galactica,” where deluxe-admission packages can run as high as $439 for the weekend? (Parking and hotel fees not included.)

But $814 for an inside cabin on a six-day cruise dedicated to “Veronica Mars”? After the teen-detective drama was canceled last year due to heart-breakingly low ratings? Really?

Really. In the extreme-fan universe, the diffuse love of 16 million “Grey’s Anatomy” viewers can’t hold a candle to the laserlike beam of the nearly 3 million devoted who watch the underpromoted, overlooked “Supernatural.”.

Those in the fan business know that viewers who bond with cult series don’t end their TV relationships when the closing credits roll. And they will pay to keep their love alive.

“People will say, ’ ’Grey’s Anatomy’ is the No. 1 show on TV, how come you guys don’t do a convention for that?’ ” said Erin Ferries, vice president of licensing for Creation Entertainment of Burbank, whose TV-related fan conventions and merchandise pull in sales of $6 million a year.

“But ’Desperate Housewives’ and ’Grey’s Anatomy’ are more general, mainstream-type shows, and they draw a more mainstream audience. My mom loves ’Grey’s Anatomy,’ but she certainly is not going to get on a plane and fly somewhere to sit in a ballroom for two or three days so she can meet the stars of the show,” Ferries said.

“They are very clued in to things that are new. They are early adopters, and they are computer literate and computer savvy.”

So it follows that once hooked, cult TV fans are likely to take their obsessions to the Web. And once they have dished on televisionwithoutpity.com about their favorite “Smallville” episodes or written “Stargate SG-1”/“Buffy the Vampire Slayer” crossover fan fiction on livejournal.com, they are often ready to bond in person.

Homemaker Sandy Schabert and husband Dan Daugherty, a software engineer, are members of the Mile High Browncoats, a Denver-based group that throws monthly “shindigs” to celebrate “Buffy” creator Joss Whedon’s short-lived “Firefly” series, its follow-up film, “Serenity,” and all things Whedonesque.

They were among a half-dozen Mile High Browncoats who came to San Diego for Christy Black’s “Browncoat Cruise,” where fans hobnobbed with cast members, exchanged “Serenity”-and “Firefly”-themed gifts and sent up prayers to the entertainment gods that Captain Mal Reynolds and his intergalactic crew would someday ride again.

They may not get their stories, but Schabert and fans like her will get their DVDs, their merchandise and their conventions whether their shows go on or not.

“You have to have talent that wants to participate, and some of these smaller shows that fly under the radar lend themselves to that,” said Creation Entertainment’s Ferries. “You have people who are more willing to do anything they can to gain more exposure for their shows.”

Which is why devilish actor James Callis of “Battlestar Galactica” will follow up his Comic-Con appearance with stops at the DragonCon convention in Atlanta next month and a Creation convention in Burbank in November. Jared Padalecki of “Supernatural” is booked for Orlando’s EyeCon convention in September, and cast members from the “Stargate” franchise will appear at multiple conventions across the country.

“Fans are the best and only chance for promotion that we have. They’re the best thing that we’ve got going, so we’d be foolish to turn our backs on them,” said “Supernatural” creator Kripke.

But even the transformative power of “Supernatural” fandom has its limits.

“I have sort of a kitschy sense of humor,” Kripke said. “So when I found out there was a ’Supernatural’ commemorative plate, I told my assistant to drop everything because we needed to get that plate. My favorite thing about it is, on the back it says, ’Warning, do not eat on this plate.’ ”