The U. S. Geological Survey has released details of its most recent study on the Bakken formation in the Williston Basin of Montana and North Dakota. The Survey says the formation contains mean undiscovered volumes of 3.65 billion barrels of oil, 1.85 trillion cubic feet of gas and 148 million barrels of natural gas liquids. It assessed the geologic elements of the Bakken petroleum system, including distribution of the source rock, its thickness, organic richness, maturation, petroleum generation capabilities and migration. It also looked at the type of reservoir rocks, their distribution and quality and the character of traps and time of their formation. The estimate represents undiscovered, technically recoverable oil and associated gas resources; it contains no calculations about the volumes of oil that could be economically recovered from the Bakken. Instead, it lays out the scale of the formation’s potential. In general, they concluded that undiscovered resources in the Bakken are in a continuous reservoir that includes all three members and that’s present throughout the entire oil-generation window, an area that covers roughly 20,000 square miles in northeastern Montana and northwestern North Dakota. Notably, in 1995 the Survey estimated that the Bakken contained only 150 million barrels of recoverable oil. The dramatic change in the resource base is due to horizontal drilling. Today, operators access Bakken oil through long-reach multi-lateral horizontal wells. EOG Resources, an operator very active in the play, has reported that its horizontal Bakken wells in North Dakota have averge lateral lengths of 5,000 feet and cost $5.25 million completed. Up to 10 stages are fractured in a lateral. To read the U.S.G.S. fact sheet on its Bakken assessment, click here. by Peggy Williams, Senior Exploration Editor, Oil and Gas Investor Contact me at