The oil pay was encountered in Miocene sandstones, and two subsequent sidetrack bores also encountered oil in reservoir intervals of a similar age.

"The drilling result is encouraging, however, the well was drilled in a structurally complex subsurface area and in a zone where seismic imaging data is of only moderate quality. Further seismic reprocessing and appraisal drilling will be necessary to evaluate the size and significance of the discovery," said Steve Bell, president, exploration and business development.

Puma-1 is located on Block GC 823, 140 miles from the Louisiana coast and eight miles from the company's Mad Dog development. The well was drilled to a total measured depth of 19,034 feet in a water depth of 4130 feet. Technical data was taken from the straight hole and sidetrack bores.

BHP Billiton has a 33.34% interest in Puma with BP (operator) 51.66% and Unocal 15%.

In 2003 BHP was involved in several large discoveries in the GoM. The company currently holds a 44% interest in the Green Canyon Block 653, which includes the Shenzi-2 well.

Located in water depths of 4,238 feet and drilled to a total depth of 25,500 ft, the well encountered approximately 500 feet of net oil pay in a 1,250 ft gross hydrocarbon column of lower Miocene reservoir sandstones.

Along with partner Woodside BHP Billiton also hit a 500ft net oil pay in the deepwater Atwater Valley Block 574 Neptune-5 appraisal well amongst a gross hydrocarbon column of around 1,200ft.

BHP Billiton shares closed yesterday at $11.59.