Unleaded aviation gasoline. An aviation gasoline fuel blend includes an unleaded aviation gasoline base fuel, with an effective amount of selected alkyl benzenes to improve the functional engine performance to avoid harmful detonation sufficient to meet or exceed selected standards for detonation performance requirements in full scale aircraft piston spark ignition engines designed for use with Grade 100LL avgas. Selected alkyl benzenes such as 1,3-dimethylbenzene, and/or 1,3,5-trimethylbenzene, or other mixtures thereof, may be used. Suitable alkylated benzenes may include a mixture of xylene isomers. Aromatic amines, such as m-toluidine, may also be added to increase MON. Base fuels may be a high quality aviation alkylate, or may be a commercial iso-octane, or a mixture of high quality aviation alkylate enhanced by commercial iso-octane, and may include iso-pentane or butane or both iso-pentane and butane in sufficient quantity to provide appropriate vapor pressure for the final fuel blend.