How many seasons of Glee do they expect with it going so fast?

Glee is a nice music drama, and I wonder how many seasons are there.

A4: Glee has been finished its third season and they have signed up for 4 seasons at least. I have just finished complete seasons 1-3 on Glee dvd online sale. If the story lines get better, probably more will be coming.

comes from: https://twitter.com/christinajey/status/219712491901566978