Describe are preferred formulations for Avgas meeting the requirements for use in aircraft, including requirements established under ASTM standards and by the Federal Aviation Administration. In one embodiment, a binary mixture of 1,3,5-trimethyl benzene (mesitylene) and isopentane is used to provide a MON of at least 100, and more preferably at least 102. In other embodiments, the amounts of mesitylene and/or isopentane may be changed, and other fuel components are included. These various Avgas formulations are thereby adjusted to meet a variety of requirements as to octane rating, RVP, cold start, and other fuel characteristics.