From the Sydney Morning Herald:
http://www.smh.com.au/news/0108/17/text/world5.html

Oracle of Delphi was powered by gas
Date: 17/08/2001
By Roger Highfield in London

The ancient Greek Oracle of Delphi, whose priestess offered predictions and
advice on the issues of the day, made her prophecies because she was high
on gas, a four-year study has concluded.

The Oracle was the most important shrine in ancient Greece. It was a site
of pilgrimage for those seeking guidance from Apollo's mouthpiece, the
Pythia, who gave cryptic answers to such matters as lifting a curse,
selecting a leader or building a new colony. Perhaps her best-known
utterance was to Oedipus, who was told he was fated to kill his father and
marry his mother.

Numerous Pythias held sway over the Greek world for more than a millennium,
from 800 BC, or earlier, until the oracle was destroyed by the Romans in AD
381.

In the August issue of Geology, scientists report that they now understand
the source of their inspiration in the temple of Apollo, the ruins of which
still stand outside the modern village of Delphi on the slopes of Mt Parnassus.

Their first clues were provided centuries ago when the temple's high
priest, Plutarch (AD 46-120), explained how the Pythia became "filled with
divine breath" due to gaseous emissions. Later the Oracle's power began to
wane because the source of the emissions was running out.

Pythia was said to sit on a three-legged stool, holding a laurel branch,
where she became gripped by the spirit of prophecy while inhaling vapours.
Like Plutarch, other ancient authorities refer to a fissure in the bedrock,
a gaseous vapour and a spring.

But scientists dismissed the notion of intoxicating vapours as the source
of the revelations a century ago when French archaeologists failed to find
a large fissure or cavity under the temple, or any other supporting evidence.

Now scientists have discovered two geological faults, intersecting directly
beneath the temple, and measured fumes rising from a nearby spring.
Anaesthetic gases were found in sediments deposited by the springs.

Professor Jelle de Boer of the Wesleyan University in Middletown,
Connecticut, working with Dr John Hale, an archaeologist at the University
of Louisville, Kentucky, give a full account in Geology this month of the
four-year study that has identified faults at the site of the Oracle and
has also pinpointed the emissions responsible for the Pythias' trances.
These were light hydrocarbon gases from bituminous limestone.

Professor de Boer and colleagues found ethane, methane and ethylene in
spring water near the Oracle. The euphoric effects of sweet-smelling
ethylene, which was used as an anaesthetic in the last century, match
Plutarch's description of the smell of the gas the Pythia inhaled.

Science can never determine exactly how the Oracle made her prophecies,
Professor de Boer acknowledges. But it can show that the ingredients to
back up the traditions really exist.

The Telegraph, London