Another technological development is Supercritical Geothermal Systems (SGS), which utilizes a natural reservoir and a supercritical fluid (extremely hot water that exists between fluid and gaseous states). Although supercritical water is hotter than regular geothermal fluids, this technology is only viable in places with volcanic hydrothermal activity like Kenya, New Zealand, Japan, and Iceland. Proponents of SGS argue that it is an extremely efficient and powerful way to generate electricity because supercritical water is more penetrative and faster than normal geothermal fluids. Opponents say that it faces challenges like corrosion and abrasion from the supercritical fluid, intense pressure causing tool deviation and unpredicted fracturing, and dependence on pre-permeated rock which limits extraction locations.