The value of a contract held by Leighton Holdings for work on the Gorgon natural gas project has more than doubled to nearly $1.8 billion.

As an example of the rising costs for the Chevron-operated project, Leighton said on Monday changes had been made to reflect an increased scope of work that provides more flexibility and faster delivery.

Leighton Contractors is carrying out earthworks and installing concrete and underground drainage, pipes and cables at the massive project in north Western Australia.

The company began the work September 2010 under a contract worth just over $800 million.

Leighton said on Monday the changes to the contract take its value to $1.789 billion.

In December, Chevron increased its cost estimates for the Gorgon project in north Western Australia from $43 billion to $52 billion, due to labour costs and productivity issues.