Fox just put in an order for two more seasons of The Simpsons, ensuring that it will exceed Gunsmoke's 20-year run to become the longest-running primetime series ever. Here's why it may never end.

The Simpsons still has a ways to go before it can surpass the amount of episodes Gunsmoke produced; due to then-longer seasons, the western banked 635 episodes (whereas the current Simpsons renewal would bring it to 493). However, we have full faith that Fox will continue to keep The Simpsons on the air long enough to outlast even that record. How can we be so sure?

· The show still does all right in the ratings. Don't mistake us—The Simpsons is hitting all-time lows this season. Then again, so are many network shows this year. The difference is that The Simpsons is the 8 p.m. linchpin for a night of animation that helps anchor the higher-rated Family Guy, and Fox would never sacrifice such an ideal lead-in. Hell, even King of the Hill managed to stick around for thirteen seasons based on Fox's Sunday night strategy.

· The voice actors may eventually become expendable. In 1998, the show's six main voice actors threatened to quit if their pay wasn't upped from $30,000 per episode. In response, Fox immediately scheduled auditions to replace them, and a deal was reached (subsequent negotiations over the years raised their pay rate to the current $400,000 per episode). In this case, The Simpsons' decades-long ubiquity may work against it—if Fox wants to cut costs and fire the original cast, they'd surely be able to find new actors raised on the show who could closely replicate the voices (the genius comic timing would certainly suffer, but are fans still ardent enough to make a fuss?). The network already enacted such a move in 1999, when minor voice actor Maggie Roswell (who performed characters like Maude Flanders and Helen Lovejoy) was fired after asking for a pay raise, and only hired back after several years' absence. Did anyone notice?

· The Simpsons is a billion-dollar global franchise. Fox has become even more of a corporate behemoth since The Simpsons first premiered in 1989, and it's hard to imagine they'd ever devalue one of their few properties that can keep a comparatively enormous pace. At this point, it almost doesn't matter what ratings the flagship series gets—not when its merchandise continues to sell all over the world, or when a feature-length movie version produced well past the show's peak makes well over $500 million.

Someday, then, when NBC is running ten hours of Today (leading straight into a four-hour block of Jay Leno, Conan O'Brien, Jimmy Fallon, and Howie Mandel), you can be certain that The Simpsons will keep on keepin' on. And this is where we would post our favorite Simpsons episode (the Gamblor one, natch), but Hulu has cruelly yanked every old episode off their service, keeping only the latest five instead. If only it aired constantly in syndication or something!