Talk:Delphi
This is just a note, but there have been convincing theories that the vapors the oracles inhaled consisted mainly of ethylene, a common hydrocarbon gas that was found in the petro-chemical rich layers of sediment surrounding Delphi. Ethylene, more potent and flammable than nitrous oxide (laughing gas), when inhaled in moderation can produce a trancelike state. the gas could have risen through fissures created by the many intersecting fault lines that run through the site.
Also, during the last years of Delphi's significance there were reports of a major earthquake that shook the region, which may have played a factor in the vapor being suddenly closed off or redirected somewhere else. That would explain why a short while later the oracle pronounced that Delphi was no longer a medium for prophecies. The general mindset is that the oracle was bribed to discredit the site, mainly because of the rise of Christianity.