Nigeria and the island state of Sao Tome and Principe have invited tenders for oil exploration in offshore fields between the two nations.

Both countries have invited energy companies to tender for the right to prospect for oil, or gas, in nine offshore blocks in the area known as the Joint Development Zone (JDZ).

The JDZ in the Gulf of Guinea was formed after the two states failed to agree on the demarcation of their borders in 2001.

The Joint Development Authority is charged with managing the development of oil wells in the zone.

Sao Tome will receive 40% of the revenues generated and Nigeria - already Africa's largest oil producer - will get 60%.

Sao Tome is one of the world's poorest countries. It does not currently produce oil and it hopes revenues from the JDZ will help turn around its economic fortunes.

The oil exploration licensing process was deferred from November because of a dispute over a small area of the zone which has now been resolved.