GAMI G100UL Unleaded Avgas Flying in a Van’s RV-14


Considering the agita surrounding the long-running search for a lead replacement in avgas, it’s not surprising that it’s often overlooked that GAMI’s G100UL unleaded, 100-octane avgas has been flying for more than a decade. What’s more, it received FAA STC approval for every known spark-ignition aviation engine at AirVenture 2022.

In this video, produced by Larry Anglisano—editor in chief of sister publication Aviation Consumer and frequent KITPLANES contributor—builder Jon Sisk discusses his reasons for building the Van’s RV-14 and, in particular, his experience using G100UL fuel. It’s worth noting that he had written into his operating limitations a note saying that both 100LL and, specifically, G100UL were approved fuels for his airplane.

This bears repeating: Recent comments from the alphabet groups seem to suggest that Experimentals are somehow beholden to using “approved” fuels, such as legacy 100LL. The catch is that GAMI’s G100UL is approved under an STC, and Experimentals have no TC to apply the S to! But rare is the set of operating limitations that explicitly calls out which fuels are “approved.” Such wording in the operating limitations for an Experimental category aircraft is unnecessary and can potentially muddy the issue.

Sisk describes flying his IO-390-powered RV on both conventional 100LL and G100UL by running one fuel in each tank and then testing under difficult conditions—high-power climb, for example—to demonstrate that the engine doesn’t really act any differently with the G100UL. (Aside from the fact that’s it’s not gaining lead deposits as it flies.)

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Marc Cook
Marc Cook is a veteran special-interest journalist who started as a staffer at AOPA Pilot in the late 1980s. Marc has built two airplanes, an Aero Designs Pulsar XP and a Glasair Aviation Sportsman, and now owns a 180-hp, steam-gauge-adjacent GlaStar based in western Oregon. Marc has 5000 hours spread over 200-plus types and four decades of flying.


  1. I’m guessing the answer will be “Fine.”
    But I’ll ask the question anyway.
    “How well does a Rotax run on this unleaded fuel?”


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