Italian energy giant Eni has completed the long-planned acquisition of Neptune Energy for nearly £4billion.
Eni has acquired the firm's entire portfolio, except Norway, which is going to Var Energi (a subsidiary of Eni), and Germany.
Around 2,000 people were employed by Neptune between Aberdeen and London and the completion of the deal is expected to have no major impact on the workforce.
Announcing the closure of the deal on Wednesday evening, Eni said: "Through this transaction, Eni integrates a high-quality and low carbon-intensity portfolio with exceptional geographic and operational complementarity to its own.
"The acquired assets include Neptune’s participation in the Eni-operated Geng North-1 gas discovery, offshore Indonesia, announced in October 2023.
"The acquisition is strategic in terms of increased gas production in North Africa, where Eni consolidates its position as the leading international energy company, and in Northern Europe, where the transaction opens up new CCS opportunities.
"Eni regards CCS as a key lever in its decarbonisation strategy and there are further possible synergies with the projects Neptune is pursuing in Norway and the Netherlands."
As well as acquiring the Cygnus gas field, Eni will also own Neptune's carbon and capture storage (CCS) sites won during last year's licencing round.
Neptune won rights to operate SNS (Southern North Sea) Area 1 BC05, SNS Area 7 Caister Bunter, and SNS Area 5 Bunter BC13, partnered with Exxon Mobil.