Oil giant Shell is to begin talks on taking Britain's biggest oilfield out of service, BBC Scotland has learned.
Brent Bravo, one of the four main platforms in the oilfield
Shell said it was looking to set up a new structure to manage the four platforms in the Brent field, which is located 115 miles off Shetland.
The company said it wanted to consult widely on options for what happened when oil and gas reserves ran out.
Shell denied a claim from the offshore union OILC that workers had been told decommissioning could start by 2010.
The news came on the day Shell reported a record annual profit for a UK-listed company - £13.12bn.
The results follow a year in which the cost of crude jumped from below $45 a barrel to break the $70 mark.
Brent, Britain's biggest oilfield, has been producing oil and gas for 30 years and provides the benchmark price for North Sea crude.
Managers on Brent's four oil platforms have recently been briefing workers that major changes are on the way.
The company wants to treat the Brent platforms as a separate entity and is seeking to recruit a new asset leader to carry out the task.
A spokeswoman said: "The remit for that will be to ensure the remaining potential is maximised and look at the best possible option for eventual natural depletion.
"Decommissioning will be one possible option, but we're looking at all the possible options through feasibility studies."
The company said no firm timescale has been set, but widespread consultation would be taking place.
Shell wants to avoid the protests that surrounded its attempts in 1995 to decommission the Brent Spar loading facility by dumping it in the Atlantic.
The OILC said workers had been told at meetings on the platforms that decommissioning would start on the Alpha, Bravo and Delta platforms in 2010.
It is expected to be complete in about five years, then work on winding down Charlie would start, the union reported.
OILC chief Jake Molloy said: "The field is quite mature and the lads realise that it won't last forever, but it was only today when we heard about the £13bn profits that things began to hit home.
"They couldn't understand why the company were looking at decommissioning after this. Why not greater investment or why not asset sales?"
He said the Forties field has been transformed after being bought by independent operator Apache from BP.
Shell said it would consider this option.
Kourosh Bassiti, an independent oil consultant based in Aberdeen, said the Brent field was coming to the end of its life.
Speaking on BBC Radio's Good Morning Scotland programme, he said: "It's been a major field in the North Sea and has been operating for 30 years.
"Oil prices are high and one wonders why not wait a bit longer to squeeze more oil out of it.
"I'm sure Shell will look at it very carefully and it's going to be five to 10 years before we see the full effect of it."