How much damage does ignited oil do?
Ignited oil seems to do 2 damage per player unit standing in it, according to this Steam guide:
Oil patches from pipe leaks, oil barrels or oil grenades can be detonated with a single projectile (bullet) and will do 2 damage to all player units standing in it. (WHAT ABOUT ENEMIES ? DOES 5 damage to enemies).
This quote can be found in the last part of the guide, "Miscellaneous damage mechanics related observations".