If you have a newer model, with the remote unlock built in to the ignition key, press the button that looks like a trunk opening. This will open the tailgate but leave the other doors locked. Otherwise, press the Unlock button TWICE - this will unlock ALL doors, including the tailgate.
You can open the driver's door and press the "unlock" switch on the armrest. This should unlock all the doors, including the rear hatch. If it doesn't, your solenoid that operates the lock needs to be replaced. For that, see your Subaru dealer.
lights are on
You can not open the rear hatch door from the inside.
Lift straight up while pulling on the door open handle. Once it click, pull towards you "feeding" the door handle out of its socket.
Solved the problem myself. Have to disassemble rear panels inside rear hatch until you find cable leading to gas tank door. About a hour or two. Replug plastic unit that opens gas door. Later glued it in place so this may not happen again.
Use the spare key or call a locksmith.
I have a 1998 Subaru Legacy Outback wagon and have the same problem. I climbed in the back and removed the back panel on the hatch door. Then I noticed the latch on the locking mechanism was getting stuck halfway. I wound up climbing into the back every time and moving out of the stuck position every time I wanted to open the hatch door. About a month ago a friend who borrowed my car noticed that if you pressed the unlock button on the front passenger side door it would unlock. I was very surprised when I found this out, but it worked. I'm not sure if that's a fluke with just my car, but it might work for you. Otherwise you could try climbing into the back like my first method. Good luck!
On the floor by drivers door floor mat
The rear hatch on a 1998 dodge durango won't open
Unlock it from inside the car with the door lock.
you turn on the car put the parking break on open the door slam in shut with the lock on(you dont need tpo slam) open it up and on the keypad by the handle type in a password and click your key car finder thing
remove the panel from the inside of the rear hatch door and check to make sure the latch mechenism is secure if not push or pull the leads to open hatch door then try to reconnect them