Chinese firms are revving up their dealmaking machines in the hunt for overseas energy resources.

In the latest move, Sinopec, the country's top oil refiner, in November agreed to pay $3.54 billion for a 30-percent stake in the Brazilian unit of the Portuguese oil company Galp Energia SA. The deal comes after its earlier purchase of a 40-percent interest in the Brazilian unit of the Spanish oil company Repsol YPF SA for $7.1 billion.

Meanwhile, the China National Offshore Oil Corp. has recently completed acquisition of Opti Canada, a Calgary-based oil sands producer, for $2.1 billion.

In the third quarter of 2011, Chinese energy firms were responsible for nine cases of overseas mergers and acquisitions (M&As). The involved capital amounted to $2.668 billion, accounting for 48.3 percent of the value of total outbound M&As, according to data from the Beijing-based Zero2IPO Research Center.

China has continued to gain strong influence in the global mining sector against a background of increasing activity in the acquisition of overseas resources," said Jeremy South, global mining leader at Deloitte Touche Tohmatsu Ltd., in a recent report.

He added that now is a good time for M&A activity because of a slight rebound in the price of resources after huge declines in recent months.

"However, Chinese companies need to find the right partners because the mining industry is a highly risky business and most Chinese companies lack experience of overseas business management," he said.