Chinese scientists have discovered that carbon dioxide is more efficient to use in fracking than water.

Fracking is the controversial process in which water or other fluids are injected into underground rocks at high pressure to release oil and natural gas deposits.

U.S. environmentalists have denounced the process because of the huge amounts of water needed, the contamination of underground water supplies, and small earthquakes it triggers.

In a new report in the journal Joule, scientists from the Chinese Academy of Sciences and China University of Petroleum discovered that using CO2 instead of water resulted in as much as 20 times more oil.

"These real-world results revealed that as compared to water fracturing, CO2 fracturing is an important and greener alternative," especially in arid areas where the water has to be trucked in, the report says.

Carbon dioxide is the main greenhouse gas blamed for global warming.

The scientists say the CO2 used in fracking would stay underground and not be released into the atmosphere.

ALSO READ: Scientists Find Gold-Studded Fungus in Western Australia

The scientists say further research is needed as well as the winning over of cooperation from the industry. (VOA)