Parker and Stone with the late voiceover actress Mary Kay Bergman

Comedy Central general manager Bill Hilary said: "We look forward to continuing the wild ride that began with South Park as we tap further into the artistic genius of this extraordinarily creative team."

The deal goes in to effect from September. Broken down, it will see Parker and Stone come up with at least 10 new episodes of the adults-only irreverent comedy each year.

The duo are also to launch a live-action series in 2001, continue series development and look into a partnership agreement for the potential syndication of South Park.

Creative freedom

Although the new contract was described as a multi-million dollar deal, the duo said they had decided to stay with Comedy Central for artistic reasons - not money.

"For the last three years we have been exceptionally lucky to have our show on a network that respects creative freedom,'' said Parker.

"We've realised it is this freedom that has made us happiest. That's why we decided to stay with Comedy Central."

The network has a reputation for developing new and innovative comedy. One of its most popular shows, Win Ben Stein's Money, has been re-made for Channel 5 in the UK with Jeremy Beadle.

Robin Williams kicks up a South Park storm at the Oscars

South Park, featuring the antics of foul-mouthed children Cartman, Kyle, Kenny and Stan, - and their equally dubious parents - debuted on Comedy Central in August 1997.

At its peak - two years ago - the show attracted some 6 million viewers. But the new season, which began on 5 April, has been bringing in between 2.5 million and 3 million viewers.

In the UK, South Park also hit the nation's TV screens on Channel 4 and Sky in summer 1997, repeating its US success.

Last year, Parker and Stone propelled South Park into cinemas with South Park: Bigger, Longer, Uncut.

Blame Canada - the expletive-filled song from the movie - was nominated for an Oscar at this year's Academy Awards, where actor Robin Williams managed to perform it without causing offence.