The extension is part of a contingency plan to ensure continuity of diesel and petrol supply to customers in the event the project is delayed.

Caltex is revamping its Sydney and Brisbane refineries to deliver the next generation of clean fuels. But it has conceded that it may not have the facilities in place by the 2006 deadline owing to the industry-wide shortage of materials and skilled labour.

In April, the company committed an additional $100 million to accelerate the project and cover design changes.

The funding has been used to increase the size of the project team, introduce double and around-the-clock shifts and place Caltex contractors on supplier sites to expedite delivery.

Caltex managing director and chief executive officer Dave Reeves said the environmental impacts of continuing to supply to 2005 fuel standards in the new year would be minimal.