Shows don't start much smaller than "It's Always Sunny in Philadelphia." But the gloriously offensive series about five selfish, petty do-nothings has grown into one of cable's most successful comedies -- and a model for FX's other sitcoms.

It could work for other networks, too. The show, which owes part of its success to a boost from "Taxi" star Danny DeVito, returns Thursday for its seventh season. It was the third highest-rated basic cable comedy last season in the crucial 18-49 demo, behind only "South Park" and "Futurama."

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The "Always Sunny" model calls for FX to take the smallest initial financial risk possible -- but allow every other kind. It appeals to creators willing to trade big paychecks for creative freedom. And it only works because FX allows that freedom even when shows turn bizarre, upsetting, or potentially infuriating.

If the risks pay off, the rewards can be huge. The trio behind "Sunny" -- Rob McElhenney, Charlie Day and Glenn Howerton -- split just $1 million to act, write, produce and star in its seven-episode first season in 2005. McElhenney, the show's creator, kept his job as a waiter.

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But under their current deal, they'll divide $40 million total for the next three seasons, assuming the show goes to ten.

"We knew relative to the business that for people that were writing, executive producing and starring, and for me directing ... we knew that ultimately it was low," McElhenney said of the first-season pay. "But we knew we owned a good chunk of the show and we were going into business with FX as the owners. What FX gave us in the beginning was a way to make our show the way that we wanted to do it."

The show is a giddy attack on traditional sitcoms, with their likeable characters, traditional setups and punchlines, and aversion to controversy. The new season finds the gang staging a baby funeral in a scheme to fool the IRS.

"I will say this," McElhenney said. "That there has never been, nor will there ever be, a sitcom on television where they have a baby funeral. We're the only one."

FX has applied the "Sunny" model of low starting pay but high creative freedom to all its comedies -- including "Wilfred," "The League," "Archer" and "Louie." (It announced a new comedy [5] from three "Sunny" writers -- the animated "Unsupervised -- just hours before Thursday's "Sunny" premiere.)

How far does the freedom go? FX president John Landgraf says he has never told a show it can't do something, no matter how distasteful he personally found it.

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Louis CK (above), who writes, directs and stars in every episode of "Louie," has taken the low-cost, high freedom model to both extremes: He doesn't wear makeup on the show. Actors wear their own clothes. He covers plenty of dangerous topics, but also goes for long stretches without a joke, preferring to be thoughtful, reflective, or absurd. Last season included a long, joke-free description of Jesus' crucifixion.

"I'm definitely paying Louis less than he would be making at a network," Landgraf said. "The difference is, Louis couldn't do what he's doing at a network. And if he did, it would get canceled after 13 episodes. If I can keep him on the air for seven years, I'm going to pay him a lot more money than he could make at a network."

Landgraf sees only one problem with the "Always Sunny" model: It only works, so far, for comedies. Dramas are expensive enough that they have to meet a certain ratings threshold. But the lower cost of comedies means the the network can renew even low-rated ones, if they hold promise.

He could easily have cancelled "Sunny" after its first season, which averaged just 1.1 million total viewers -- but cost only $575,000 an episode, including salaries.

Instead of shelving the show, Landgraf suggested a new investment: adding DeVito to the cast. He had served previously as president of the star's Jersey Television.

Curiosity seekers wondering what DeVito was doing on the show stayed with it, and word-of-mouth has helped it grow to last season's 2.1 million total viewers, down slightly from the previous year's.

"Louie," "Archer" and "The League have all posted second season improvements, and the first-season "Wilfred" is already FX's second-highest rated comedy, after "Sunny."

This season the show has more buzz than ever, thanks to McElhenney's decision to gain 50 pounds for his role. He thought it would funny for his vain character, Mac, to become spontaneously fat this season, and was sick of seeing sitcom stars get better looking every year. (Other castmates, including his wife, Kaitlyn Olson, declined to join the weight-loss adventure; McElhenny has now lost almost all of the weight.)

The closest Landgraf ever came to telling him he couldn't do something, McElhenney said, was during the first season, which covered racism, abortion, underage drinking, cancer, guns, Nazi memorabilia and child molestation. The network president suggested he change a molester from a priest to a gym teacher, McElhenney said. He agreed to the change.