The government has said that "fracking" for shale gas can resume in the UK, despite the process triggering two earth tremors near Blackpool last year.
Here's a guide to fracking and why it is so controversial.
What is fracking?
Hydraulic fracturing, to use its full name, is a way of obtaining methane gas from shale rock.
The gas is found in layers of relatively weak sedimentary rock, usually several kilometres underground.
To obtain the gas, a well is drilled into the ground and pumped full of water, sand and chemicals under high pressure.
This causes the rock to crack, or fracture, releasing the gas for extraction.
Why is fracking important?
It is considered a relatively cheap way of obtaining an important energy supply.
According to a report by the International Energy Agency in 2011, the global use of natural gas is expected to account for more than a quarter of the world's energy demand by 2035.
Fracking can release this gas quickly and, it is argued, more efficiently than other methods of releasing natural gas.
In 2010, the BBC reported BP's former BP's former chief executive Tony Hayward as describing shale gas as a "game changer" in energy supply.
Why is fracking controversial?
The pumping of chemicals into the ground can risk contaminating ground water, which can lead to pollution of an area's water supply and damage the environment. Opponents of fracking also argue it can cause risks to air quality and surface contamination from spills.
In addition, the process can lead to disturbances within the Earth's crust, such as tremors and earthquakes.
What happened in Blackpool?
Test fracking was being carried out by the Cuadrilla company near Blackpool in 2011, but was halted when two earthquakes were felt at the surface - one of magnitude 2.3 in April, and one of magnitude 1.5 in May.
What have experts said about these earthquakes?
A report was commissioned by the government earlier this year on the future of fracking in the UK. One of its authors, Professor Peter Styles from Keele University, said: "[Cuadrilla's experts] said there was a very low probability of other earthquakes during future treatments of other wells".
He continued: "We agree that [last year's] events are attributable to the existence of an adjacent geological fault that had not been identified. There might be other comparable faults, (and) we believe it's not possible to categorically reject the possibility of further quakes."
Another of the report's authors, Brian Baptie of the British Geological Survey, said there is only a "very small" risk of damage from earthquakes caused by fracking.
"Even in a low seismic country like the UK, we get roughly 16 earthquakes [like these ones caused by fracking] in the UK each year... We think the maximum magnitude that might occur could be around magnitude three. That's based on the analogy with coal mining, and there's a long history of coal mining earthquakes over previous decades and the largest of those had a magnitude of three."
AP Photo, Ed Andrieski
What has the government announced about the future of fracking?
It has said that Cuadrilla can resume fracking in Lancashire. But operations will restart under stricter controls to monitor and prevent seismic activity.
The report commissioned by the government earlier this year recommended that four precautions be adopted when fracking resumes:
- all injections of fracking fluid must include a preliminary injection, followed by monitoring
- the growth of fractures in the shale should be monitored
- operations should monitor seismic events in real time
- operators should observe a "traffic light" regime, with quakes of magnitude 0.5 or above triggering a "red light" and an immediate halt, followed by remedial action.
Cuadrilla has said it hopes to resume operations as soon as possible.
How has the government justified its decision?
Ed Davey, secretary of state for energy and climate change, said: "Shale gas represents a promising new potential energy resource for the UK. It could contribute significantly to our energy security, reducing our reliance on imported gas, as we move to a low carbon economy. My decision is based on the evidence. It comes after detailed study of the latest scientific research available and advice from leading experts in the field."
What other reaction has there been?
Tony Grayling, head of climate change and communities at the Environment Agency, which regulates fracking in the UK, said: "We are satisfied that existing regulations are sufficient to protect people and the environment in the current exploratory phase. We have also established a shale gas unit to act as a single point of contact for industry to ensure there is an effective, streamlined approach for the regulations that fall within our responsibility."
Leila Dean of Greenpeace criticised the decision, saying: "George Osborne's dream of building Dallas in Lancashire is dangerous fantasy. He is not JR Ewing and this is not the US. Energy analysts agree the UK cannot replicate the American experience of fracking, and that shale gas will do little or nothing to lower bills. Pinning the UK's energy hopes on an unsubstantiated, polluting fuel is a massive gamble and consumers and the climate will end up paying the price."