Tom Baxter is a senior University of Aberdeen lecturer in chemical engineering.
But Mr Baxter is also a business unit director with Genesis Oil and Gas Consultants, which has been asked by the Scottish Government to assess the cost of decommissioning platforms.
He believes they should be cleaned and left in the sea.
Mr Baxter argues in a paper to the think tank, Options for Scotland, that platforms do not have to be removed.
He said: “It seems decommissioning is happening solely because legislation says it has to.
“However, it will cost between £40 billion and £50bn – half of which will be paid for by the taxpayer.
“And you have to question what they get out of it. It’s an eye-watering cost. Platforms could be left and could become habitats for sea life.
“Marine life does not care where such constructs come from, they just see it as a place to live.
“We have seen this work in the USA and it could happen in the North Sea.
“That is not to say that we can’t remove anything that might be harmful to the environment, but I’ve yet to meet an environmentalist who says clean metal is harmful to the sea.
“I understand that decommissioning will create jobs, but it doesn’t give value for money and I would say I have exposed a very inconvenient truth.
“The platforms have been in the water for decades and have not proved to be a hazard for marine life or for vessels.
“I do not see why that would change.”