The graph, left, illustrates the explosion of growth in horizontal drilling in the U.S. This can largely be attributed to the increase in shales plays that are now profitable because of technological advances, such as the those in the Bakken and Utica. Hydraulic fracturing has increased significantly in horizontal wells, which reduce surface disruptions and increase production rates.
You can read more about fracing and horizontal drilling here:
Notice the increase in drilling rigs since 2009. As of October 21, 2011, there has been a +354 increase in US working drilling rigs YOY. Over the same 12 month period, Canada increased rigs by +78, and International rig counts are up by +54 (International number may be underestimated due to difficulty collecting data from Russia and China).