I've had a few nights after Taco Tuesday where gaseous emission almost put me in a trance...(sorry couldn't resist)
But seriously, I think the general consensus is that like modern horoscopes or the verses of Nostradamus, the Oracle of Delphi just uttered some vague random phrases that could be interpreted a hundred different ways. A Emperor who wanted to go to war would speak to her, she would utter something like "On the harvest moon, the light of Jupiter will shine on the fields of grain." The Emperor would interpret this as some great victory by Fall. And if he lost the battle...well then the Oracle's supporters would just say he misinterpreted it and the Oracle was speaking of a bountiful harvest.
https://www.storynory.com/7-king-croesus-and-the-oracle-of-delphi/
https://www.freerepublic.com/focus/chat/3698267/posts?page=9#9
Only 2 posts before the first fart joke!
And couldn’t the source of the vapors simply exhausted over time?