The oil industry's response to an oil price downturn has typically been to explore opportunities for mergers and acquisitions. Royal Dutch Shell's stunning tilt at acquiring BG Group represents what bankers and investors predict will be the first flag in the ground in a new phase of dealmaking.

The two companies stunned the City on Wednesday morning with news they have agreed a deal valued at around £47 billion, following reports the night before that Shell was in talks to acquire BG.