“Inert” is the term used to describe substances that are not chemically reactive. However, reactivity is dependent on context. Historically, the noble gases (helium, neon, argon, krypton, xenon, and radon) were referred to as inert gases. Nitrogen (N2), argon (Ar), and carbon dioxide (CO2) are commonly used inert gases in the wine industry because these have little or no reactivity with wine. These can be used individually or as a mixture in varying proportions. Oxygen (O2) is reactive with many chemical compounds in wine and is therefore not inert.