A key North Sea oil pipeline is expected to be shut down later on Saturday, because of a planned strike at the Grangemouth refinery.
BP is to shut the Forties pipeline, which brings ashore a third of the UK's daily crude oil output, in response to the stoppage, set to start on Sunday.
Production at the refinery has already halted ahead of the strike.
The authorities say there is enough fuel to go round, but some garages in Scotland are already running out.
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The two-day stoppage by up to 1,200 workers is over changes to pensions.
Production at the refinery, which is Scotland's main fuel supplier, ceased on Friday afternoon ahead of the strike.
BP is now preparing to shut down the pipeline because the Kinneil terminal, its final destination, depends on electricity and steam from the refinery.
That power has so far still been provided, despite the production shutdown at Grangemouth. But Grangemouth's owner, Ineos, says the Unite union is refusing to maintain power and steam at the refinery when the strike begins.
BP said it expected that power would not be available from Saturday evening.
Without that power, 700,000 barrels of oil a day cannot be brought ashore and more than 70 platforms in the North Sea could be forced to stop production.
'Wholly disproportionate'
Industry body Oil and Gas UK said closing the pipeline could cost an estimated Ј50m a day in lost production - with the Treasury taking half that hit.
Chief executive Malcolm Webb issued a last-ditch plea for both sides to agree on measures which would keep the Kinneil plant running and minimise disruption to supplies from offshore.
He said the potential effect of the Grangemouth strike on UK oil and gas production was "wholly disproportionate" to the scale of the dispute.
Drivers have been urged not to potentially exacerbate the situation by filling up their tanks unnecessarily.
There have already been reports of shortages, rationing and queues at some forecourts.
A Scottish Government spokesman said: "One of the most important messages to give is that people should not change their normal fuel buying patterns.
"We urge the people of Scotland to be sensible and only to buy the fuel that they need.
"We encourage people to make the journeys they require to and to use public transport."
Scotland's First Minister Alex Salmond earlier said BP was releasing stocks from Grangemouth diesel which should help ease supply problems.
He added that substantial fuel cargoes, from ports including Rotterdam and Gothenburg, were "more than enough" to supply Scotland for next week.
(BBC)
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