In well-lit hangar and separated into nice clean glass containers, it’s easy to tell the difference between 100LL aviation gasoline and kerosene-based turbine fuels like Jet A. In the field, not so much: Fuel tanks are dark places, and shining a flashlight onto a liquid rarely helps identify what it is. Draining some fuel into a sampling cup and comparing it to what you’re looking for may not help, either, since jet fuel typically is clear (or straw-colored) and may not appreciably change the tint of 100LL.
Jet A does smell differently than aviation gasoline (and nothing smells better than avgas!)—its odor is more like kerosene or diesel fuel. But odor alone won’t help determine if there’s Jet A in your avgas. Instead, you’ll have to investigate even further. There are two basic ramp tests a pilot can use to determine if there’s any jet fuel in the avgas.
