Woodside, Australia's second-largest oil and gas producer, 34%-owned by Royal Dutch Shell, said a delay in the start-up of BHP Billiton's $1.1 billion (£555.3 million) Neptune oil and gas project in the US will reduce forecast production.

Output in 2008 will be down by an estimated 150,000 barrels of oil a month until the "issue" with the platform has been resolved.

BHP, the project operator will revise the start-up schedule for the Gulf of Mexico project after "structural anomalies" in the platform led to the evacuation of all workers.

Crews started returning to the platform yesterday after BHP confirmed that it was safe.

"Further inspection and assessment is under way to determine the appropriate course of action to mitigate the anomaly," BHP said.

Start-up was originally due by the end of 2007 and the budget was last year revised up from $850 million.

"The operator is undertaking structural inspection and analysis before advising of any required action," Woodside said today. It added that it could not estimate when the project may start up.