Examples of injection wells regulated by the
Railroad Commission of Texas: 
- Wells injecting waste arising out, of or incidental to,
drilling for or production of oil, gas, or geothermal
resources (Class II).
- Wells injecting waste arising out of, or incidental to, the
underground storage of hydrocarbons other than
storage in artificial tanks or containers (Class II).
- Wells injecting waste arising out of, or incidental to, the
operation of gasoline plants, natural gas processing
plants, or pressure-maintenance or repressurizing plants.
The injected waste fluid (usually salt water) may be commingled
with wastewaters from gas plants, unless those waters are
classified as hazardous waste at the time of injection.
(Class II.)
- Wells used for the enhanced recovery
(secondary recovery) of oil or natural gas (Class II).
- Wells used for the underground storage of hydrocarbons
that are liquid at standard temperature and pressure
(Class II).
- Salt-mining/brine injection wells
(Class III).
- Wells used for in situ combustion of fossil
fuels (in situ coal and lignite gasification)
(Class V).
- Injection wells associated with geothermal
resources (Class V).
- Injection wells for remediation of an aquifer
contaminated by unrefined-petroleum-product spills
(Class V).
- Geothermal wells used in heating and
aquaculture (Class V).
- Injection wells to recover petroleum products from
tar-based sands (Class V).
