It confirmed to investors during a site visit that the two fields would provide roughly 11 trillion cubic feet of gas. The fourth train will involve the installation of a fourth LNG tank on the island, with a new pipeline to feed the project.

The environmental impact assessment has already been lodged with the state government, with front end engineering design on the expansion to begin late this year.

Speaking to investors, greater Gorgon area manager Colin Beckett said that successful appraisal of pre-2009 fields discovered in the area and development drilling on existing discoveries gave Chevron the confidence to declare a fourth train viable without affecting the input into the first three trains.

With the addition of the fourth train, the project would have a capacity of 20.8Mtpa, meaning the expansion would essentially crown the Gorgon LNG project as the largest in Australia by capacity.

Beckett also said gas from the fields was low in carbon dioxide and "high in deliverability", adding that the fourth train would be leveraged off existing infrastructure on the island to achieve a train at the lowest cost.

Costs have been somewhat of a hot topic in the LNG space recently, with operators seemingly falling over themselves to tell media and government about the high cost of developing LNG projects in Australia.

It is believed Chevron is undertaking a review of its budget at Gorgon, but there was no mention of costs associated with the fourth train in a presentation to investors, who were left to speculate.

Beckett kept the $43 billion price tag on the project and said first LNG was still slated for 2014, with the project review to be done and dusted by the end of the year.

Earlier this year, Chevron upstream vice president George Kirkland said along with a 20% strengthening of the Australian dollar since the project was approved in 2009, it had experienced construction delays due to weather, while the Australian Marine Complex at Henderson, south of Perth, had not been as productive.

"We've also seen Australian labour costs trending higher. This could impact both construction and management services.

"Because there are a number of variables in play, we currently have a detailed cost review underway."

The latest round of concerns on LNG costs began in May, with BG Group confirming a $US5 billion ($A4.8 billion) cost blowout at the QCLNG project.