Oil giant BP is to shed about 350 jobs at its North Sea headquarters in Aberdeen as part of a restructuring of its operation.
BP has suffered a profit slump despite rising oil prices
The company said 250 of those affected would be onshore BP staff, while the remaining 100 were contracted workers.
The company said offshore and Norwegian operations would not be affected by the reorganisation, which will take place over the next six months.
BP saw its third quarter profits for the period to September slump by 45%.
The company said the changes were intended to improve efficiency and meet the challenges of declining production and rapidly rising costs in the North Sea.
It has a total onshore staff and contractor workforce in the UK of 2,100 at present.
A spokesman said the move was "regrettable", and that the exact number of positions to be cut would be announced in the new year.
He added: "Regrettably, the company anticipates that the changes may result in the loss of some BP staff and contractor positions which support its operations in the UK.
"The company will consult with staff over the coming months and into 2008 on how these changes will be implemented and seeks their views on how the impact on jobs can be minimised or mitigated."
The job cuts are expected to be made by March.
Unions have expressed their concern at the announcement and called for an urgent meeting with management.
Graham Tran of the Unite Amicus Union said: "We did expect job losses but clearly nothing on this scale.
"This is a massive and devastating blow to the employees of BP and a surprise to the industry in general.
"Having said that, we still have good times in the North Sea and there is no reason as to why the skills of these people should be lost to the industry."
Mr Tran called on BP to set up an industry network system to allow workers to advertise their skills and expertise to other companies.
"Failure to do this would be a betrayal to the loyal service of the people at BP," he said.
Jake Molloy, of the Offshore Industry Liaison Committee (OILC) union, said he was also shocked at the number of jobs that were to be cut and spoke of his concern about the knock-on effect for the entire BP workforce.
"Who is going to provide the support for the workers that was previously considered necessary?" he asked.
"We did anticipate casualties, just not as many as this. It is going to come as a big, big shock to many people at BP.
"That goes beyond restructuring, that is cutting back."
BP also confirmed that staff at its Kinneil terminal near Grangemouth could be affected by the job cuts.
The company produces around 350,000 barrels of oil per day from the UK Continental Shelf.
In 2004 it was producing 550,000 barrels per day.
Profits at BP were down to $3.88bn (£1.89bn) for the three months to the end of September from $6.98bn a year earlier, while oil and gas production for the period was 4% lower.
BP revealed earlier this month that it would overhaul the firm in a bid to improve its standing by getting rid of certain levels of management and attempting to consolidate its existing business.