On 24 May 2017, INEOS entered into an agreement to purchase DONG Energy's oil and gas business, which includes assets and operations in Norway, Denmark and the United Kingdom.

The purchase price is USD 1.05 billion plus a contingent payment of up to USD 250 million. In 2016, DONG Energy's production was 100,000 boe per day. Estimated reserves is around 570 million boe. The acquisition is subject to approval by the relevant authorities. Thommessen's assistance is related to the Norwegian oil and gas business and assets.

The Thommessen team comprises Rune Solberg, Stein Kimsås-Otterbech, Christian Hals, Claus Severin Mørch and Cathrine B Hetland.