Exxon said the discovery, made at the Redtail-1 well, will add to its previous estimate of over 8 billion barrels of total oil and gas resources on the Stabroek Block.

However, the company did not specify how much it estimates would be recoverable from this well and did not outline development plans for it.

"Exxon has a good problem in that it has a large number of discoveries to choose from, which allows it to optimize and choose the highest return discoveries to develop," said Anish Kapadia, director of energy at Palissy Advisors.

Kapadia said Exxon could look at selling off some of the discoveries that may not be as important for it as they would be for other smaller companies.

Exxon operates the Stabroek block as part of a consortium with Hess Corp and China's CNOOC Ltd and began production on it ahead of schedule in December.

The new find continues the Exxon-led consortium's long string of discoveries in Latin America's newest crude producing nation and underscores the importance of Guyana to Exxon for increasing its future oil output.

Exxon also said it encountered high-quality oil-bearing reservoirs while drilling at its Yellowtail-2 well and was evaluating them for development.

(Reporting by Shruti Sonal in Bengaluru; Editing by Shailesh Kuber and Ramakrishnan M.)

By Shruti Sonal