Unleaded aviation gasoline. High quality aviation alkylate, or similar base fuel is blended with selected alkyl benzenes to improve the functional engine performance to avoid harmful detonation in aircraft piston engines. Monoalkylated benzenes such as toluene and ethylbenzene are utilized in combination with dialkylated benzenes, such as xylenes. Aromatic amines, for example p-toluidine and m-toluidine, may be added to increase MON. Alcohols such as ethanol and/or methanol may be added in effective amounts to produce unleaded AVGAS which meets a required freeze point. Amounts of toluene to p-toluidine, and/or of the amount of p-toluidine to m-toluidine may be in a controlled ratio in amounts effective to produce unleaded AVGAS which meets a required freeze point. Isopentane and/or butane may be included to provide a required vapor pressure profile. Manufacturing may be achieved using an additive concentrate including aromatic solvents, aromatic amines, and alcohols.