There are developed and potential oil and gas fields on the Navajo Nation. The oldest and largest group of fields is in the Paradox Basin in the Four Corners area. Most of these fields are located in the Aneth Extension in Utah but there are a few wells in Colorado, New Mexico and Arizona. The first well was drilled in the Aneth Extension in 1956. In 2006 the Paradox Basin fields were injected with water and carbon dioxide to increase declining production. There are also wells in the Checkerboard area in New Mexico that are on leased land owned by individual Navajos.