Oil companies from emerging economies are responsible for more than half the sector's biggest mergers and acquisitions by value this year as state-controlled companies have exploited western groups' relative weakness to secure control of resources.

Emerging economy buyers, led by Chinese and Russian companies, paid for $24.2bn of the total $48bn value of the 50 largest oil and gas deals in the second quarter, according to PwC, the professional services firm. Such companies had accounted for one-fifth of the total value of deals last year.

M&A advisers expect state-controlled groups to remain active in the takeover market in the coming months, benefiting from sponsor governments' financial strength and less pressure than western companies over short-term performance.