To avoid this fate, ExxonMobil initiated a major strategic thrust into clean energy by focusing on natural gas, a low-carbon alternative to petroleum. This strategic move is an example of horizontal integration. In 2009, Exxonmobil bought XTO Energy, a natural gas company, for $31 billion. XTO Energy is known for its ability to extract natural gas from unconventional places such as shale rock, where huge deposits have been found recently in the United States.