It was observed again and again in the movie Avatar that humans could not breathe the air present in Pandora. So it can be assumed Oxygen was not present in Pandora. But again the human fires which erupted in the Hometree bombing, wouldn't be sustained if there was no Oxygen at all. So what were the components present in the air of Pandora? On the other hand if there was Oxygen, why could not the humans breathe there? So was the atmosphere in Pandora Oxygen filled or Oxygen free?
Quoting from Pandora wiki:
Pandora's Atmosphere components:
Why can't human breathe in Pandora:
So Oxygen is present there and that's why combustion is possible.