The Bakken Oil Shale Play is located in the Williston Basin. The Bakken Shale
Map below is from the USGS. As you can see, North Dakota, Montana, Canada, and South Dakota are in this region.
Click the map to go to a website that has additional details of Bakken Shale.
Bakken Shale Map
The majority of the oil is being found in the sanish / three forks
area which is located in the middle of the Bakken Shale. Geologists think that the three forks formation is a separate
reservoir which could yield even more oil! For more information of the three forks formation, go here - http://www.bakkenshale.net/threeforkssanish.html