Shell has made a deepwater gas discovery at its Leopard-1 well in license BCD10, offshore Gabon in West Africa.
The company identified a gas column in the Leopard-1 well with around 200m of net gas pay in a pre-salt reservoir.
The Leopard-1 well, which is situated 145km off the Gabonese coast, west of Gamba, was drilled 2,110m deep to a total vertical depth of 5,063m.
Shell operates the license with 75% stake and CNOOC holds the remaining interest.
Both firms are undertaking an appraisal programme to identify the volume of the resource.
Shell Upstream international director Andy Brown said: "Shell has been exploring in Gabon for more than 50 years.
"This latest deepwater discovery is a testament to the innovation of our explorers in pursuing new plays, and application of our global sub-surface expertise.
"We are proud to be sharing this success with CNOOC Ltd, our partner in the licence."
Shell said the frontier discovery follows recent deepwater exploration successes for Shell Exploration in the Gulf of Mexico and Malaysia.
In September 2014, Shell started oil production from its Cardamom subsea development in the deepwater Gulf of Mexico.
The company has recently started oil production at the Gumusut-Kakap floating platform, which is in waters of up to 1,200m, offshore Malaysia.