https://www.hdot.org/debunking-denial/d ... s-engines/
The argument seems to be that there are certain limitations on producer gas that would make them not use it. That being, they are more explosive and harder to start up. I have seen a response to the first point from Fredrich Berg here:
Producer gas contained from 18% to as much as 35% carbon monoxide. If all one wanted to do was kill people, one need never actually fill a chamber completely with 35% CO--just let enough of the CO-rich producer gas blow into the chamber to achieve a level of about 10% average CO and then shutoff the flow from the generator. So long as the level of CO is below 12% (which is still extremely lethal) there will be NO danger of explosion.
viewtopic.php?f=2&t=5693&p=38442#p38442
I haven't seen a response to the second point though. From my limited understanding of this stuff, it seems like the greater efficiently otherwise might make up for it being harder to start up. Although I don't have experience with starting up producer gas, so if anyone knows about how hard it is to start up producer gas, I would be very interested in what you have to say.
On top of all that, it seems like whatever limitations producer gas might have, it seems pretty absurd that they would use gasoline or diesel for mass murder when they need to conserve it for a war they are fighting. Although part of the narrative surrounding the holocaust is that the Nazis were so intent on mass murdering Jews that they were willing to jeopardize the whole war to carry it out. That's just how crazy they were. I find all that very hard to believe.