FYI - I think Amazon had this a few weeks back but now the seasons are up to 25-27.99.
If you're looking to save a few bucks here ya go. Great show!
http://www.buy.com/search/q/search_store/4/querytype/video_dvd/loc/322/display/col/dclksa/1/Oz%20Season%20HBO.html?adid=17654&dcaid=17654