Applying enhanced oil recovery techniques to mature oil fields, such as through waterflooding, to recover additional reserves or prolong production after primary recovery methods have run their course. By increasing production efficiency, EOR methods can prolong the economic life of older fields by as much as 30 years. Three major categories of EOR have been found to be commercially successful to varying degrees: (1) Thermal recovery, which involves the introduction of heat such as the injection of steam to lower the viscosity, or thin, the heavy viscous oil, and improve its ability to flow through the reservoir; (2) Gas injection, which uses gases such as natural gas, nitrogen, or carbon dioxide that expand in a reservoir to push additional oil to a production wellbore, or other gases that dissolve in the oil to lower its viscosity and improves its flow rate; (3) Chemical injection, which can involve the use of long-chained molecules called polymers to increase the effectiveness of waterfloods, or the use of detergent-like surfactants to help lower the surface tension that often prevents oil droplets from moving through a reservoir. Chemical techniques account for less than one percent of US EOR production. Each of these techniques has been hampered by its relatively high cost and, in some cases, by the unpredictability of its effectiveness.