The inner cabinet on Thursday gave the green light for hydrocarbons (oil) exploration and drilling in three regions in Greece.

The cabinet, chaired by Prime Minister George Papandreou, gave the go-ahead for oil exploration in an area in the Gulf of Patras, a second area west of Ioannina, in Epirus prefecture, and in the region of Katakolo in Ileia prefecture, with an estimated potential of 250-300 million barrels over a period of 15-20 years.

Environment, Energy and Climate Change deputy minister Yiannis Maniatis, who briefed the cabinet, the formal, open door invitation of interest will be issued on 1 January 2012, while in the meantime Greece will brief the international community on its decision.

"This is the first time that Greece is doing this, and everything will be conducted with full transparency," Maniatis told reporters after the meeting, which took place in the parliament building.

The entire process is slated for completion in a year's time, with the announcement of the winner of the tender, while in 18 months' time activities will commence with the installation of the required drilling equipment.

According to estimates, the oil deposits in the Gulf of Patras are estimated at 200m barrels, in the Ioannina region at 80m barrels and in Katakolo at 3m barrels over a 15-20 year timeline.

Calculated with the international forecasts for oil prices, which are expected to reach $150 a barrel in the next few years, the estimated value of the three deposits is approximately 25bn billion euros over a 15-year-period, of which 13-14bn euros are anticipated to enter the state coffers.

At the same time, procedures are being completed for the commencement of seismic studies for possible hydrocarbon deposits in the entire region of the Ionian and southern Crete, given that early indications have been "encouraging".