Marathon Oil Corporation (NYSE:MRO) is an international exploration and production company. Based in Houston, Texas, the Company had net proved reserves at the end of 2012 of 2 billion barrels of oil equivalent in North America, Europe and Africa.
Chesapeake Energy (NYSE:CHK) is the second-largest producer of natural gas, a 11th largest producer of oil and natural gas liquids and the most active driller of new wells in the United States.
Shell is a global group of energy and petrochemicals companies. With around 90,000 employees in more than 80 countries and territories, Shell helps to meet the world's growing demand for energy in economically, environmentally and socially responsibl