Shale gas is an ‘unconventional’ fossil fuel, which means that additional procedures are required to extract it beyond regular drilling. Many such unconventional sources of oil and gas were formerly too difficult (or uneconomic) to extract until recent advances in drilling technology. A combination of directional drilling and a process called hydraulic fracturing have made accessible large amounts of natural gas locked up in the tight pores of shale formations at depths of 2km or more. Successes in the United States have driven prospecting across Europe—drilling began earlier this year in Lancashire. It is estimated that the UK could be producing around 10% of its current gas needs from shale if it can be extracted at a commercial rate.