The Bakken Formation is an oil-producing shale formation underneath North Dakota, Montana, and parts of Canada. In recent years, horizontal drilling and hydraulic fracturing techniques, combined with higher prices for crude oil, have led to rapid increases in oil extraction from shale formations like the Bakken Formation. As of late 2011, North Dakota was the fourth largest oil-producing state, after Texas, Alaska, and California. The large increase in oil production has led to growth in employment and wages and has changed the industry profile of employment in the region.