Substances which, when added to gasoline, increase the amount of oxygen in that gasoline blend. Fuel ethanol, ethyl tertiary butyl ether (ETBE), and methanol are common oxygenates.
- Fuel ethanol: Blends of up to 10% by volume anhydrous ethanol (200 proof), commonly referred to as the “gasohol waiver”.
- Methanol: Blends of methanol and gasoline-grade tertiary butyl alcohol (GTBA) such that the total oxygen content does not exceed 3.5% by weight and the ratio of methanol to GTBA is less than or equal to 1. It is also specified that this blended fuel must meet ASTM volatility specifications (commonly referred to as the “ARCO” waiver). Blends of up to 5.0% by volume methanol with a minimum of 2.5% by volume cosolvent alcohols having a carbon number of 4 or less (i.e., ethanol, propanol, butanol, and/or GTBA). The total oxygen must not exceed 3.7% by weight, and the blend must meet ASTM volatility specifications as well as phase separation and alcohol purity specifications (commonly referred to as the “DuPont” waiver).