The Colombian government Thursday officially announced that it is to auction oil and natural exploration rights for 13 offshore blocks along its Caribbean coast on Sept. 18.

The fields, with an average of 290,000 hectares, cover almost all of the Colombian Caribbean shore except for natural reservation areas and areas already handed to different oil companies, according to the announcement by Mining and Energy Minister Hernan Marinez.

He said the area's oil and gas reserves might be rich, but that was "pure speculation" as no thorough studies have been carried out.

Previously Colombia has only discovered small reserves of oil, which with the current oil prices in the world market have not been profitable.

So far, Italy's Eni Spa, Royal Dutch Shell and Colombia's state-owned oil company Ecopetrol have requested information on the auction process, while many others have approached the Colombian government, said Armando Zamora, president of the National Hydrocarbon Agency, which is the government's oil licensing body.

The winners of the exploration rights will be the companies that offer to transfer the biggest share of oil or gas production to the government if they make a commercial discovery. Once licensed, they will have a 10-year right to explore the area and rights to produce oil until the field is depleted.

The South American country has long been under-explored because of its poor security situation. It has only just managed to maintain its oil production levels to guarantee oil self-sufficiency for the coming years through an investment plan tapping deeper into developed oil blocks and heavy oil.

Last year Colombia produced 529,314 barrels of oil per day, slightly higher than 2005. If current consumption and production trends continue, the nation will become a net oil importer in 2014.