Respirometers are instruments used to measure the rate at which organisms consume oxygen. Synonyms for respirometers may include oxygen sensors, metabolic rate monitors, oxygen consumption meters, and oxygen analyzers. Some types of respirometers include closed respirometers, which measure oxygen consumption in a closed system, and open respirometers, which measure oxygen consumption in an open system. Other types include mass flow respirometers, which measure oxygen and carbon dioxide exchange, and differential respirometers, which measure differences in oxygen consumption between different groups of organisms. Respirometers are commonly used in research on metabolism, ecology, and physiology of animals and plants.