I don't know for sure but here's what I read on a Supernatural forum the other day. "after finding nothing in the TV I change the channel to TV Guide Network and they're giving "2007 TV Summer Preview" anyways the thing is I hear them saying that Supernatural was not only going to be renewed for a third season but they signed for a fourth season airing on 2008. They just mentioned it so I don't have evidence to support it but if any of you find something please share." One of the replies was "that's really cool laz! actually i think i read an article just before they announced there was going to be a season 3 with kim manners about how his agent was in talks with the network for two more years... that would include a season 4... shoot, im gonna go see if i can find the article now... but like lots of other people are saying, im just grateful for the season 3 right now!! i'll worry about season 4 later!!"

So fingers crossed! (forum mentiioned above found at link
ible-supernatural-season-4-in-2008/topic/­137­86
-780075/msgs.html )

Eric Kripke (Supernatural creator) said in an interview that he had a rough plan for 5 seasons of Supernatural (including the 2 and a 1/2 already aired); you can read the whole interview here:

link

and another interview stating that the last 4 episodes of Season 3 will begin being shown on January (2009) can be seen here:

link

YAY!

IGNORE the four episodes I mentioned; I'm in the UK (not an excuse in itself) and I mixed up what he was saying (wishful thinking) he was talking about episodes 9-12 of Season 3 beginning over there (U.S) on Jan 31st of THIS year. The stuff about the 5 seasons still stands though.