Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR₄⁺, R being an alkyl group or an aryl group. Unlike the ammonium ion (NH₄⁺) and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged, independent of the pH of their solution. Quaternary ammonium salts or quaternary ammonium compounds (called quaternary amines in oilfield parlance) are salts of quaternary ammonium cations.