In the United States, ozone-depleting substances (ODS) are regulated as class I or class II controlled substances. Class I substances, such as chlorofluorocarbons (CFCs) and halons, have a higher ozone depletion potential and have been phased out in the U.S.; with a few exceptions, this means no one can produce or import class I substances. Class II substances are all hydrochlorofluorocarbons (HCFCs), which are transitional substitutes for many class I substances. New production and import of most HCFCs were phased out as of 2020. The most common HCFC in use today is HCFC-22 or R-22, a refrigerant still used in existing air conditioners and refrigeration equipment.