Oil spills of up to 10 tonnes have been identified as one of the hazards of proposals to transfer oil between ships in the Firth of Forth. The likelihood of such a spill could be once every 20 years, according to an environmental impact statement obtained by the Scottish National Party.
The plan involves transferring millions of tonnes of crude oil for shipment to markets such as the US.
Forth Ports said new safeguards had been introduced since the study.
The environmental impact study was commissioned by Melbourne Marine Services, the Sunderland-based company behind the controversial proposals.