Shale gas is similar to coalbed methane but the gas is instead held in mudrocks and shales of low permeability. Until relatively recently shale gas was not technically or economically feasible to extract. As UK North Sea reserves decline onshore shale gas becomes a more economic proposition. To liberate the gas it is necessary to shatter the rock using a technique called hydraulic fracturing or fracking. Similar to CBM shale gas extraction involves drilling vertically into the shale formations and then horizontally to access the shale over an area.
There are numerous local environmental concerns relating to both shale gas and coalbed methane extraction including the possibility of surface and ground water pollution, noise, traffic and light pollution, seismicity and impacts on green house gas emissions.