The reserves revision follows extensive seismic, drilling and evaluation programs, according to ExxonMobil Australia chairman Mark Nolan.

“Our understanding of the geological history of Gippsland, combined with our expertise in applying the latest evaluation and modeling techniques, including the identification of direct hydrocarbon indicators utilising basin-wide 3D seismic data, has enabled us to better understand the resource available in Bass Strait,” Nolan said.

The extra gas can be extracted and transferred by the joint venture's extensive existing Bass Strait infrastructure.

The Esso-BHP 50/50 joint venture has dominated Bass Strait petroleum production for almost 40 years and has so far extracted about five trillion cubic feet of gas.

The reserves upgrade follows an announcement in June that Esso, BHP Billiton, Woodside and Santos had agreed to develop the 620bcf offshore Gippsland Kipper.

“These additions to our resource base provide an even more extensive foundation underpinning the long term strength and competitiveness of our Gippsland gas business in supplying gas to South Eastern Australia,” Nolan said.

“As a result of our confidence in the substantial resource remaining in the basin we are planning to undertake a 3D seismic survey of the Bream Field as well as continuing a drilling program in several other fields in 2006.”