2019 art, featuring Domingo and an old roadster.

Behind-the-scenes/world-building stuff: For various reasons, I have come the the conclusion that Geoterrans would either not have access to petroleum, or at the very least, nowhere to the extent of modern-day Earth. Yet, I have sometimes drawn them driving cars recognizable to us Earthlings. The solution to this "problem" was actually rather obvious, and I should have thought of this sooner... inside Domingo's car, like most Geoterran vehicles, is what would be recognizable to us as a Diesel engine, and these vehicles run on biodiesel fuel.

This makes sense not only as a petroleum/gasoline alternative, but as being in line with a lot of the rarely-explored but canon themes of "alternative technological development".