Brunswick Group and Finsbury are advising the blockbuster $70B acquisition of the UK's BG Group by Royal Dutch Shell.

shellBG Group, a multinational based in Reading, UK, with major operations in the liquefied natural gas space, was spun off of British Gas as Centrica in 1997.

The cash and stock sees Shell paying a 52% premium on BG shares and comes amid a global decline in oil prices. "The result will be a more competitive, stronger company for both sets of shareholders in today's volatile oil price world," Shell chairman Jorma Ollila said in a 30,051-word press release announcing the deal April 8.

On the PR front, Finsbury is supporting Shell's global communications team regarding the deal. Managing partner James Murgatroyd leads the London-based Finsbury team, assisted by natural resources lead Dorothy Burwell.

Lachlan Johnston heads external communications for BG, which is counseled by Brunswick Group. Brunswick London partner Michael Harrison, who once covered the energy sector, among others, while a journalist for The Independent and Evening Standard, leads Brunswick's account.

Shell said it expects to save $2.5B per year by 2018 on "synergies" with BG, including cost savings and reductions in exploration spending. It expects charges of $980M over the first three years.

The resulting company's market cap is pegged at $240B, behind Exxon Mobil's $360B atop the energy sector, excluding state-owned operations.