In the HC book / compilation of blog posts, Roberto Muehlenkamp states the following:
Wood could to a large extent be replaced as a combustion agent by gasoline or other liquid flammables. (p. 486)
He does this, presumably, because even according to his own highly distorted calculations only 27%-51% of Treblinka’s fuel requirements could have been supplied by the wood commando. Moreover, supposing that gasoline was the main fuel allows him to decrease the anticipated quantities of ash.
Muehlenkamp claims (table on p. 486) that it would have taken between 4 and 11 liters of gasoline to cremate one body.
Revisionists, on the other hand, have consistently maintained (at least as far back as Ivan Lagace) that gasoline is a poor fuel for body incineration, due to its tendency to burn off very quickly.
What do experts say? Well, according to the book The Analysis of Burned Human Remains (download it here):
People often assume that gasoline alone will accomplish great damage to a human body. Gasoline burns off very quickly, however, and damage from the flames will only rarely exceed splitting and charring of the dermis. In one case in the author’s experience, a woman was doused with a gallon of gasoline and set alight while dressed in a shirt, denim pants and cotton socks, lying on a sandy soil surface. She died from shock but her skin was nearly intact, penetrated to any degree only at her ankles where the cotton socks, secured by a leather belt, absorbed enough gasoline to continue to burn for some minutes (Icove and DeHaan, 2004).
It’s worth noting that naked bodies (without clothing to absorb the gasoline) will be even harder to incinerate with gasoline than clothed bodies are.