Roc Oil, operator of the TP/15 Joint Venture, said the ENSCO-53 jackup drilling rig arrived at location on Friday and commenced drilling on Saturday.

"During the next week the well is expected to penetrate the potential reservoir, reach Total Depth and run a preliminary suite of logs," the company said.

The Twin Lions-1 surface location is approximately 8km north of the Cliff Head-3 surface location in the adjacent WA-286-P.

Twin Lions-1 will be drilled, as a vertical hole, to a total depth of 1,540 metres subsea to test the Twin Lions Prospect which is estimated to hold reserves in excess of 370 million barrels.

The TP/15 Joint Venture comprises of Hardman Oil & Gas Pty 30%, AWE Oil (Perth Basin) 25%, Roc Oil (WA) 20% - operator, Westranch Holdings (a subsidiary of Norwest Energy NL) 10%, Arc Energy NL 5%, Voyager Energy 5%, Bounty Oil and Gas NL 5%.