PETROCHEMICAL giant Ineos, which owns the Grangemouth refinery, has agreed a deal worth up to £1 billion to buy a string of North Sea oil and gas fields from Danish group Dong Energy.

Ineos – controlled by British billionaire Jim Ratcliffe – said the move will propel it into a top 10 company and the biggest private group operating in the North Sea.

It will boost its so-called upstream division, seeing it add a portfolio of production, development and exploration sites off the coast of Denmark, Norway and the West of Shetland area.

Ratcliffe said that on completion of the deal, which is expected in the third quarter, it will bring a full complement of highly experienced oil and gas personnel, with around 440 staff transferring from Dong Energy to Ineos.

Ratcliffe, chairman of Ineos, said the business was a “natural fit” for the group as it expands its upstream arm.

He added: “Dong Energy’s oil and gas business is a natural fit for Ineos as we continue to expand our upstream interests. This business is very important to us at this stage of our growth plans and we are delighted with the expertise that comes with it.

“We have been successful in our petrochemical businesses, focussing on operating our assets safely, efficiently and reliably and we intend to do the same with our oil and gas assets.

“We are keen on further growth and already see lots of opportunity within this impressive portfolio when it transfers to Ineos.

“The business complements Ineos’ existing upstream activities which were formed on the acquisition of both Dea’s and part of Fairfield’s UK portfolio in 2015.

“Including these oil and gas acquisitions, alongside the very recently announced plan to acquire the Forties Pipeline System from BP – pending regulatory and third party approvals – Ineos is the fastest-growing entrant in this important energy basin.”

He said the business he has acquired has a strong portfolio of long life assets, producing 100,000 barrels of oil equivalent per day in 2016 and with around 570 million of commercial and potential oil and gas reserves across the Danish, Norwegian and UK Continental Shelves.

Henrik Poulsen, chief executive of Dong, said: “Since the decision in 2016 to divest our upstream oil and gas business, we’ve actively worked to get the best transaction by selling the business as a whole, getting a good and fair price for it and ensuring the optimal conditions for the long-term development of the oil and gas business. With the agreement with Ineos we’ve obtained just that.”

The acquisition comes after Ineos recently snapped up a 235-mile pipeline from BP, which transports nearly 40 per cent of the UK North Sea’s oil and gas production, for up to $250 million (£193 million).

Ineos employs around 18,500 people across 105 sites in 22 countries. It is the 200th largest business in the world, with sales of 40 billion US dollars (£31 billion) a year. When it launched in 1998, the group had 400 staff and annual sales of $200 million (£154m).

Now it has taken another big move into the oil and gas sector by agreeing to buy Dong Energy’s portfolio of North Sea assets in a deal worth up to £1bn. The better-than-expected $1.05bn price will be topped up by a further $250m, payable between 2018 and 2020 to the Danish energy group, which is cutting its historic ties to fossil fuels.

Ineos director Tom Crotty said the chemical giant’s latest move into the oil and gas sector was agreed after over a year of talks – and further deals are likely.

“We’re still looking. We’ve made no secret of our ambition to grow. I’d be surprised if we don’t do a few more deals,” he said. “We’re talking to quite a few different people. Some of them might come to fruition, some of them might not.

“We are buying because we think we’ve gained experience in the last 20 years in petrochemicals on buying assets that are no longer wanted by big oil majors. We are very good at asset management and we think the North Sea has reached the point where you need good asset managers who are going to exploit them properly and make sure we get maximum economic recovery from those fields.

“This is very much a separate business to Grangemouth. There is a side benefit that we are more in control of our upstream feed stocks, but it is really about an opportunity to develop in the North Sea. We have laid out that ambition and this is our third acquisition in the North Sea and hope there will be more to come.

“Some of the assets we are buying today are actually very young. The West of Shetland fields we are acquiring opened up in 2016 and there are some new fields that haven’t even started yet that we have bought shares in. We think there is more to go on that before we look further afield.

“We hope we can run them, not necessarily more cheaply, but we hope more efficiently. We can manage our costs very well and we have the attention to detail to make sure we get all the oil and gas that’s there.”

Ratcliffe founded Ineos in the late nineties by buying up key chemicals assets, and appears to be following a similar strategy in his reinvention of the group as a major player in gas productions.

Ineos bought the Grangemouth petrochemicals refinery from BP in 2005, and earlier this year paid the oil major over £200m to buy the Forties pipeline system.

The North Sea’s oldest and largest oil and gas pipeline transports 450,000 barrels of oil every day, of which 20 per cent flows to Ineos’ Grangemouth refinery.

The company has also become the UK’s third largest shale producer after snapping up the entire onshore portfolio from Engie, formerly known as GDF Suez.

In contrast, Dong’s exit follows a new focus on offshore wind power.