The hydrocarbon-rich shale plays of the northern tier of US states are the main attraction for Northern Oil and Gas, which explores for and produces oil and natural gas on properties in the northern US. The company keeps overhead and risk down by purchasing minority, or non-operating, interests in producing oil and gas projects. With leaseholds on more than 171,130 acres in the Williston Basin (the Bakken and Three Forks oil and gas fields in North Dakota and Montana) the company in 2012 reported proved reserves of 67.6 million barrels of oil equivalent.