Petroineos say all refining in Grangemouth has finished.
More than 400 people are losing their jobs, as the refinery closes down.
It is being turned into a fuel import terminal.
It's the last remaining oil refinery in Scotland.
The Scottish Government has urged UK Government ministers to consider nationalising the plant.
Speaking when redundancy letters were sent to workers, Unite general secretary Sharon Graham said:
“It is a quite frankly a national disgrace that Petroineos has been allowed to press ahead with this needless act of industrial vandalism.
There is a clear plan for the future of Grangemouth in place. Yet the UK and Scottish governments are missing in action."
Iain Hardie, regional head of legal and external affairs for Petroineos, said:
He said: "Petroineos has invested £50m in creating a modern import and distribution terminal capable of receiving finished fuels by sea for onward distribution to customers around the country.
"From today, we will be importing all the products necessary to meet Scotland's demand for transport fuels."
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