Twelve North Sea gas fields have been sold by the Russian oligarch who bought them earlier this year but was forced by the UK Government to sell them.
Ineos, the chemicals giant that controls Grangemouth refinery and petro-chemicals plant, has taken them on.
This is its first move into owning oil and gas assets.
There are indications its chairman and controlling shareholder Jim Ratcliffe intends to buy more.
The 12 fields, mainly in the southern North Sea, were sold in March by German firm RWE to the LetterOne company controlled by Mikhail Fridman.
They represent around 8% of UK gas production, including the Breagh and Clipper South fields.
The UK Energy Secretary before the UK election, Ed Davey, told LetterOne in April that it had to sell them again.
He said it was not in UK interests to have the fields at risk of sanctions against Russians, and threatened to revoke the owner's operating licence. The sale had to take place by 20 October.
Jim Ratcliffe of Ineos said: "We are pleased to acquire a strong portfolio of natural gas assets and bring on board a highly successful and experienced North Sea industry team.
He said of the gas fields: "They are high quality, low risk assets and they come with a highly experienced management team. Whilst no decisions have yet been made, we will continue to evaluate other opportunities in the North Sea.
"Ineos has been very open about its intention to make strategic investments in the North Sea and this acquisition is our first step in fulfilling this goal. It will also help our UK petrochemical assets to have ongoing access to competitive energy."
Ineos is also investing in onshore unconventional gas projects in the UK, though these are proving controversial.
It has invested heavily in the shipping, docking and processing facilities to bring fracked gas from the USA to Grangemouth and to a Norwegian processing facility.