While the Coco-1 well produced 26 degree API oil and associated gas to surface during open hole testing of two separate intervals in the sub-salt sequence, one test encountered sand influx during testing while the other was affected by mud losses to fractures during drilling.

Roc said the well will be suspended as an oil discovery, but it will be re-entered and tested more comprehensively as soon as practical within the next six months.

The Simmons 80 rig will move on to drill the Sesamo-1 well later this month and Arroz-1 in August, the last two wells of Roc's drilling program in Cabinda South.

Three earlier wells in the program were plugged and abandoned for being non-commercial, while the first well, Massambala-1 - the first drilling effort in onshore Angola for more than 30 years - made a heavy oil discovery.

Roc plans to drill up to six shallow wells to appraise Masmbala during the second half of this year and planning for this programme is underway.

Massambala is estimated to contain between 50 million and 500 million barrels of in-place oil resource.

Roc has a 60% working interest in the Cabinda South Block joint venture. Its partners are Force Petroleum (20% interest) and Angolan state company Sonangol P&P (20%).