British company IGas Energy reported there may be as much as 170 trillion cubic feet of shale natural gas reserves in its Bowland Shale license area in Lancashire.
Oil Change International, an advocacy group concerned about hydraulic fracturing, said Tuesday the only way to verify the reserve estimate is to start drilling.
"Once again the devil is in the detail," OCI Contributing Editor Andy Rowell said in a statement. "Because of the nature of fracking, even to get a reliable estimate on reserves could take some 50 wells to be drilled."
Drilling practices employing hydraulic fracturing, known also as fracking, gives energy companies access to oil and natural gas reserves that weren't accessible using previous drilling technology. OCI said only a small percentage of the gas surveyed by IGas Energy may be commercially viable, however.
Fracking critics are concerned about the potential for some of the carcinogenic compounds used during the process to leach into groundwater.
The British government last year lifted a ban on fracking and enacted a risk-control measure based on a "traffic light" system. Risk-control measures were in response to small tremors associated with fracking campaigns in 2011.