Amid fracking bans, Colorado discusses the controversial practice

LOST HILLS, CA - MARCH 24: Pump jacks are seen at dawn in an oil field over the Monterey Shale formation where gas and oil extraction using hydraulic fracturing, or fracking, is on the verge of a boom on March 24, 2014 near Lost Hills, California. Critics of fracking in California cite concerns over water usage and possible chemical pollution of ground water sources as California farmers are forced to leave unprecedented expanses of fields fallow in one of the worst droughts in California history. Concerns also include the possibility of earthquakes triggered by the fracking process which injects water, sand and various chemicals under high pressure into the ground to break the rock to release oil and gas for extraction though a well. The 800-mile-long San Andreas Fault runs north and south on the western side of the Monterey Formation in the Central Valley and is thought to be the most dangerous fault in the nation. Proponents of the fracking boom saying that the expansion of petroleum extraction is good for the economy and security by developing more domestic energy sources and increasing gas and oil exports. (Photo by David McNew/Getty Images)

Fracking has allowed oil and gas firms to tap new supplies and has led to a boom in some U.S. states but environmentalists have concerns. The BBC's Kim Gittleson reports from a Colorado fracking meeting.

This summer, the United States overtook Saudi Arabia and Russia to become the world's largest oil producer.

And that's all due to one thing: the rise of hydraulic fracturing, or fracking.

It's a technique designed to recover gas and oil from shale rock by drilling down into the earth, where a high-pressure water mixture is injected into the rock to release the gas inside.

Fracking has allowed oil and gas firms to tap new supplies, and has led to a boom in some U.S. states like North Dakota and Pennsylvania.

But it has also drawn controversy, with environmentalists warning about negative health consequences.

That has led some towns to ban the practice.

The BBC's Kim Gittleson went to Colorado to find out more.

She begins her report at a public meeting about fracking in Denver.