Tullow Oil said the Carapa well offshore Guyana had struck oil at about 4 m of net pay, which analysts believe is unlikely to be commercially viable.
The discovery was located within title AC/P64 about 160 km (99 miles) northeast of the Shell-operated Prelude floating LNG facility.
Preliminary estimates show the discovery west of Heidrun Field to hold between 6.3 million and 12.6 million barrels of recoverable oil equivalents, the Norwegian Petroleum Directorate said.
The discovery is a significant one in a country that currently produces about 200,000 barrels of oil per day.
Mexican state oil company Pemex said on Dec. 6 it has discovered a deposit in southeastern Mexico that could yield 500 million barrels of crude, calling it the largest such finding in more than 30 years.
The field stretches over 2,400 sq km (927 sq miles) in the oil-rich Khuzestan province, Iran President Hassan Rouhani said Nov. 10.
Recoverable resources are estimated at between 38 million and 100 million barrels of oil equivalent, adding considerably to the area’s resource base, the company said.
Equatorial Guinea's Ministry of Mines and Hydrocarbons said the well, located in the Santonian reservoir offshore in the Rio Muni Basin, was drilled to a depth of 4,400 m.