Katakolo off-shore area in western Peloponnese comprises the only area in western Greece (Ionian zone) with a proven oil/gas-field discovery. The discovery dates back to the early 80s where recoverable reserves were estimated at 3 million barrels of oil. Limestones of Cretaceous-Eocene age, part of the Ionian zone, form an anticline structure with reservoir rock, unconformably overlain by Neogene sediments.