Over the past few years, advancements in drilling technology have opened up huge shale gas reserves in the united states. From being a gas-deficient country a few years ago, the united states, at present is awash with gas supplies. the barnett shale in north texas and the Marcellus shale spread across Pennsylvania, new york, ohio, West Virginia, and adjacent states are two of the most established and prolific shale gas-producing plays. shale gas accounted for approximately 20 percent of total u.s. natural gas supplies in 2010, and is projected to increase to 45 percent by 2035. shale gas extraction technology was pioneered by smaller companies, and the segment was mostly ignored by the international oil majors. However, with the end of easy oil and reserve restrictions in certain parts of the world, the majors recently started entering this segment.