To hydraulically fracture an unconventional gas reservoir, large volumes of fracturing fluid are injected into the production zone via the wellbore at high pressures. Fracturing fluid consists of 3 primary constituents, water, sand and other constituents.

It is the grouping of other constituents that has proven controversial. While some of these constituents are innocuous (e.g., an iron precipitation controller such as citric acid, a common food additive), others are less so (e.g., a scale inhibitor such as ethylene glycol, a principal component of automobile engine coolant). The oil and gas sector has historically regarded the composition of fracturing fluid as proprietary, but has become more transparent of late (refer to For more information section elsewhere on this webpage for link to website disclosing well-specific fracturing fluid composition).