Denbury Resources is the largest combined oil and natural gas producer in Mississippi and Montana. In 2015 it reported estimated proved reserves of 288.6 million barrels of oil equivalent, of which 98% was oil. It owns the largest reserves of carbon dioxide (CO2) used in enhanced (also called tertiary) oil recovery east of the Mississippi River, and it holds operating acreage in its two core regions, Gulf Coast and Rocky Mountains. Using CO2 in enhanced oil recovery is one of the most efficient tertiary recovery methods for producing crude oil. Denbury Resources generates substantially all of its revenue from sales of oil, natural gas, and related products.