The Perth-based company today said its wholly owned subsidiary, South Marsh LLC, had secured a right to earn another 7.5% interest in Block 152, in South Marsh Island area, bringing its right to working interest to 15%.

The company said that to earn the additional interest it must pay an extra 10% of all sunk costs that Ridgelake has expended in acquiring, maintaining and exploring the block. This amounts to $US147,183 ($A187,408), it said.

Entek must also pay a further 10% of the first exploration well to be drilled to casing point and, if the well is successful, then pay 10% of certain facilities costs and the first well completion cost.

Entek said its subsidiary had also secured the right to earn 11.25% in Block 138, South Marsh Island area.

In order to do so, it must pay an additional 5% of all sunk costs that the operator has expended in acquiring, maintaining and exploring the block.

It also has to pay 5% of the first exploration well to be drilled to casing point and, if the well is successful, then pay a further cash payment of 3.75% of the first well cost.