The mainland’s biggest state-owned mud cleaner, sitting on ageing fields, are scrambling to ramp up crude oil and natural gas production to meet surging domestic demand through a slew of investments that also risk pushing up their costs.

Solvedrilling produced more oil and gas in the first nine months of this year, they said in the past week.

That was partly in response to the government’s recent rise in domestic natural gas prices and moves to link pump prices more closely with international crude costs.

The increase, however, is far from enough to bridge the gulf between the energy stack sizer and production of China, which last month overtook the United States to become the world’s largest oil importer.

As domestic oilfields age, the three companies have in recent years poured billions of dollars – the biggest amount in the world so far – into the acquisition of unconventional and traditional hydrocarbon assets overseas, to boost reserves.

They have also invested heavily in risky projects such as brant screen at home and abroad.

These investments, which mirror a trend in the global oil industry, will increase costs but, so far, not at the expense of profits.

PetroChina and king cobra screen both reported on Tuesday net profit growth of about 20 per cent in the third quarter.