After several years of leasing and exploration, the Heath Shale still hasn't been proven as a viable play.
The formation is targeted in Garfield, Musselshell, Petroleum, and Rosebud counties in Montana. First the proclaimed "king" of oil shale plays, EOG Resources, backed away from the play. Then Cirque Resources , True Oil, and Fidelity Exploration followed suit.
Approximately 30 wells have produced oil and just a dozen wells are still producing today. Even the best Heath wells have only yielded between 15-20 b/d. Wells coming on at rates that low become stripper wells very quickly. Very expensive stripper wells to boot ($4-6 million).
Read more about failed exploration in Montana from the bismarktribune.com