Analysts have downgraded production forecasts, following global miner BHP Billiton's (ASX: BHP) fear that the Gulf of Mexico disaster will destroy the petrol growth prospects this year.

The BP oil crisis has also led to a downgrade of up to $US1 billion ($1.13bn) in earnings projections.

As announced yesterday, BHP had reduced internal estimates for up to 10 per cent growth in petroleum, and was foreseeing a flat year because of a drilling ban in the deepwater gulf.

The report was supported by analysts at UBS, Macquarie, Citi, and Deutsche Bank, who all cut their forecasts for BHP's oil output this year to almost the 158.6 million barrels of oil equivalent posted last financial year.

While the drilling ban is scheduled to end in November, it could be prolonged. It "may delay the additional seven production wells required at Atlantis North during fiscal 2011", said Deutsche Bank analyst Paul Young, who downgraded his 2010 to 11 BHP oil production expectation by 6 million barrels.

"The ban on drilling may also delay the approval and construction of the Mad Dog South and Knotty Head projects, which we expect to be sanctioned in fiscal 2011 and fiscal 2012 respectively," he said.

Citi analyst Clarke Wilkins said combined with decreased copper and iron ore production, the ban would reduce 5 per cent or $US1.1bn from his current-year revenue forecast.