the Pythia was (on occasion) a noble of aristocratic family, sometimes a peasant, sometimes rich, sometimes poor, sometimes old, sometimes young, sometimes a very lettered and educated woman to whom somebody like the high priest and the philosopher Plutarch would dedicate essays, other times who could not write her own name. So it seems to have been aptitude rather than any ascribed status that made these women eligible to be Pythias and speak for the god.
Before 200 BC, while the temple was dedicated to Apollo, there was probably only one priest of Apollo. Priests were chosen from among the main citizens of Delphi, and were appointed for life. In addition to overseeing the oracle, priests would also conduct sacrifices at other festivals of Apollo, and had charge of the Pythian games. Earlier arrangements, before the temple became dedicated to Apollo, are not documented.
The other officiants associated with the oracle are less well known. These are the hosioi ("ὅσιοι", "holy ones") and the prophētai ("προφῆται", singular prophētēs). Prophētēs is the origin of the English word "prophet", but a better translation of the Greek word might be "one who speaks on behalf of another person." The prophetai are referred to in literary sources, but their function is unclear; it has been suggested that they interpreted the Pythia's prophecies, or even reformatted her utterances into verse, but it has also been argued that the term prophētēs is a generic reference to any cult officials of the sanctuary, including the Pythia. There were five hosioi, whose responsibilities are unknown, but may have been involved in some manner with the operation of the oracle.
Experience of Supplicants:
Step 1: Journey to Delphi — Supplicants were motivated by some need to undertake the long and sometimes arduous journey to come to Delphi in order to consult the oracle. This journey was motivated by an awareness of the existence of the oracle, the growing motivation on the part of the individual or group to undertake the journey, and the gathering of information about the oracle as providing answers to important questions.
Step 2: Preparation of the Supplicant — Supplicants were interviewed in preparation of their presentation to the Oracle, by the priests in attendance. The genuine cases were sorted and the supplicant had to go through rituals involving the framing of their questions, the presentation of gifts to the Oracle and a procession along the Sacred Way carrying laurel leaves to visit the temple, symbolic of the journey they had made.
Step 3: Visit to the Oracle — The supplicant would then be led into the temple to visit the adyton,
put his question to the Pythia, receive his answer and depart. The degree of preparation already undergone would mean that the supplicant was already in a very aroused and meditative state, similar to the shamanic journey elaborated on in the article.
Step 4: Return Home — Oracles were meant to give advice to shape future action, that was meant to be implemented by the supplicant, or by those that had sponsored the supplicant to visit the Oracle. The validity of the Oracular utterance was confirmed by the consequences of the application of the oracle to the lives of those people who sought Oracular guidance.
Fumes and Vapors:
The vapor is if high importance in the Chaos Story line. Here is some info that can bring light to this mystery.
The oracle of Apollo at Delphi was famed throughout the Greek world and even beyond. The oracle - the Pythia or priestess - would answer questions put to her by visitors wishing to be guided in their future actions. The whole process was a lengthy one, usually taking up a whole day and only carried out on specific days of the year. First the priestess would perform various actions of purification such as washing in the nearby Castilian Spring, burning laurel leaves, and drinking holy water. Next an animal - usually a goat - was sacrificed. The party seeking advice would then offer a pelanos - a sort of pie - before being allowed into the inner temple where the priestess resided and gave her pronouncements, possibly in a drug or natural gas-induced state of ecstasy.
There have been many attempts to find a scientific explanation for the Pythia's inspiration. However, most commonly, these refer to an observation made by Plutarch, who presided as high priest at Delphi for several years, who stated that her oracular powers appeared to be associated with vapors from the Kerna spring waters that flowed under the temple. It has often been suggested that these vapors may have been hallucinogenic gases.
Recent geological investigations have shown that gas emissions from a geologic chasm in the earth could have inspired the Delphic Oracle to "connect with the divine." Some researchers suggest the possibility that ethylene gas caused the Pythia's state of inspiration. Traces of ethylene have been found in the waters of the Castallian spring, which is now largely diverted for the town water supply of the town of modern Delphi. However, Lehoux argues that ethylene is "impossible" and benzene is "crucially underdetermined." Others argue instead that methane might have been the gas emitted from the chasm, or CO2 and H2S, arguing that the chasm itself might have been a seismic ground rupture.
Sources and Links to more interesting info regarding The Pythia:
Oracle of Delphi