The fourth release called Thomas In Charge has so far had it's title episode confirmed to be on the DVD while the other three have yet to be revealed.
VideoETA have revealed the cover for the release which can be seen on their website and features Thomas and Gordon.
The DVD will run at 50 minutes.
Thomas In Charge hits US DVD shelves on July 12th 2011.
Thanks to SteamTeam3211 for the alert.