The Chinese government sets gasoline prices at levels designed to provide reasonable profits for state-run oil companies. It gives military support if these companies drill in hotspots such as the South China Sea. And it helps seal deals, such as a recent $400 billion Sino-Russian natural gas contract.

Investors in energy stocks often point to strong government support as reason enough to hold any or all of China’s oil giants through their listed stocks PetroChina Company Limited (ADR) (PTR), Sinopec Shanghai Petrochemical Co. (ADR) (SHI) and CNOOC Ltd (ADR) (CEO).

But the recent collapse in global crude oil prices, which the Chinese government can’t control, has punched a big hole in that reasoning. Investors now have a chance to take a hard look at Chinese energy stocks and may want to consider jumping ship before the hole gets bigger.

The fact is, China’s Big Three oil companies are riskier than other global energy stocks right now. Energy stocks in general have been steadily sinking on the 50% plunge in crude prices since last summer. But over the past three months CNOOC shares have lost 27% in value, PetroChina stock has fallen 19% and Sinopec is down 15%. By comparison, BP plc (ADR) (BP)’s shares declined 18% and Exxon Mobil Corporation (XOM) lost 7% during the same period.

China Oil Stocks are Riskier

The Chinese companies stand out because they’re facing unique and potentially intense headwinds that can make other energy stocks look a lot safer. Here are five major risk factors:

• Prices at the pump. The government is feeling the heat of public pressure over gas prices, which have not fallen in step with the crude price decline. In fact, pump prices recently jumped due to a nationwide gas tax increase. A gallon of regular cost about $4.34 a gallon in Beijing on Friday, compared to an average $2.71 in Washington, D.C. One Chinese business news portal commenter on Friday smugly recommended Chinese drivers go to Chicago to fill their tanks. When Chinese pump prices eventually fall, the oil companies will feel the pain.
• Anti-corruption crackdown. Executives at these oil companies are working in a climate of uncertainty. The unease began in 2013 when the government started detaining PetroChina executives on corruption charges. Communist Party “discipline inspection” officers are reportedly stationed at company offices. Scores of executives have lost their jobs.
• Overseas investments. In recent years — when crude oil commanded twice today’s price — CNOOC invested billions by buying an oil field in Uganda, an oil sands project in Canada and a stake in Argentina’s oil company Bridas Corporation. Sinopec invested in a Nigerian project and PetroChina bought an Iraqi oilfield from ExxonMobil.
• South China Sea. Diplomatic tension between China and its neighbors, including the Philippines and Vietnam, shadows Chinese oil company deep-sea exploration activities in the South China Sea. China claims most of the sea is its sovereign territory and, but other nations disagree, creating potential for conflict.
• Uncertain domestic supplies. China imports about 58% of its oil. Domestic wells in the Daqing oilfield in Heilongjiang Province are reportedly slowing down. Efforts to extract from domestic shale have yet to bear fruit. A report in the First Financial Daily newspaper said China’s new national petroleum reserve has four bases with more than 90 million barrels of crude, enough for just 16 days of demand. And although dozens of nuclear power plants and liquefied natural gas terminals are under construction, the country will still be dependent on imported oil for a long time, putting the Big Three at the mercy of global crude prices.

In recent days, Chinese stock analysts have been relatively quiet about the potential impact on the Big Three since crude prices plunged. One raising a red flag was Anxin Securities, which in a report commented, “In the context of plummeting oil prices, Sinopec and PetroChina’s profit margins narrowed significantly. The cost advantages of using LNG and CNG natural gas have declined, which is bad for the industry.”

Huarong Securities offered an indirect warning: “We have stressed that the impact of the fall in crude oil prices on petroleum and petrochemical companies cannot be ignored… If you want to get involved again” in Chinese energy stocks “you may want to wait for a rebound in oil prices.”

Considering the many risk factors, that seems like sound advice for investors in the big three Chinese oil stocks, PetroChina, Sinopec and CNOOC.