There are many reasons why applications by five oil-and-gas companies to prospect in the Karoo for natural gas reserves trapped in shale layers deep underground have raised public unease.

Worldwide, occasional incidents of pollution, including well-head blowouts, have raised fears about a technique called ‘hydraulic fracturing’. This is a process that has long been used to extend the life of underground reservoirs, or of ordinary wells drilled into gas deposits. In essence, a liquid containing some useful but environmentally harmful chemicals – to prevent corrosion, emulsify mud, and so on – is pumped down the well, and placed under pressure. This causes cracks in the surrounding rock, releasing trapped pockets of oil or gas.