One of the greatest oil discoveries of all time happened in North Dakota around 2008. The US Geological Service had estimated that the Bakken area of North Dakota had 4 billion barrels of oil. However, due to new rock fracturing technology, it was soon discovered that the USGS estimate was far too low. This set off a black gold rush in North Dakota and Montana for the light sweet crude oil that could now be gotten in abundance because of technology advances.
One of the first companies to capitalize on Bakken oil was Continental Resources (CLR), and they still own the largest amount of acres there. Other companies are shown in a table below along with Continental. Oasis (OAS), Whiting (WLL), Kodiak (KOG), and Northern Oil (NOG) are all big players in the Bakken oil fields.
Naturally, the stock prices have gone up and down for these companies during the oil boom. However, the amount of oil in the Bakken area could last for decades, and these companies will have plenty of time to grow during the next 20 years. I have listed the stock prices and acres of these companies as of May 18, 2012. These prices are actually significantly lower for the companies compared to a few months ago, and they are all worth buying at these levels.
It should be noted that KOG has a high PE, but they are justified in being worthwhile because they have increased their revenues year over year (2011-2012) from 13.3 million dollars to 80 million. Also, NOG is a non-operator in the Bakken area, but they are getting a percentage gain from all of their leases, and they still have a lot of potential for making money just like the rest of the oil companies.