The Toronto-listed company said an independent Competent Persons Report (CPR) showed an increase in the gross prospective resources to 5,141 million barrels of crude oil equivalent (MMBOE) from the block from a prior estimate of 3,981 MMBOE in March last year.

London-listed shares of Eco Atlantic rose 11% in early trade, while Tullow slipped 1.3%.

The report added that there were 22 prospects, potential traps that may contain hydrocarbons, identified on the block, including 11 in a geological structure known as the Upper Cretaceous.

Guyana, a global exploration hotbed, has become an increasingly important region for Tullow after a series of missteps at its flagship fields in Ghana and projects in Kenya and Uganda ran into delays.

Tullow is the operator of the Orinduik block, with a 60% stake. France's Total SA holds 25% and Toronto-listed Eco Atlantic has the remaining 15%.

In the fourth quarter, Tullow's shares were partly hit by the oil quality found in a well in the Orinduik block.

(Reporting by Yadarisa Shabong in Bengaluru; Editing by Bernard Orr)