Royal Dutch Shell announced on Wednesday its deal to acquire gas giant BG for $70bn, reported Reuters. The deal is a rare and major acquisition in the oil world. Shell’s decision was driven by its goal to close the gap on the world’s biggest oil company, U.S. ExxonMobil.

BG, which is worth $46bn, announced in a statement on Tuesday it was in advanced discussions regarding a possible offer by Shell, whose market capital is $202bn. ExxonMobil on the other hand is worth $360bn.

Shell would boost its proved oil and gas reserves by 25 percent, and give it better prospects in new projects, particularly in Australia LNG and Brazil deep water, according to the statement.