The leak is most likely the rear main seal. Have you made sure the engine is not frozen? Turn it over by hand first, best if the plugs are out of it first. Squirt some oil into the cyclinders before that, then put a socket on the crank pully and spin it over a few times. If you don't hear any strange noises than crank it a few times with the starter just to get some oil up into the lifters and rocker arms, then throw the plugs back in and fire it up.