Santos' junior partner in its promising Dorado exploration venture in Western Australia has advised of a major upgrade in the volume of petroleum thought to be held in the field despite disappointing results from exploration at a nearby prospect.

The total volume of oil and gas in the Dorado field is now put at 344 million barrels of oil equivalent (boe), up from the 283 million boe estimate given last August, reported Carnarvon Petroleum, which owns 20 per cent of the offshore permit alongside Santos.