MPs from the main opposition Bulgarian Socialist Party have demanded that the government impose a moratorium on all shale gas drilling in Bulgaria over concerns about its hazardous environmental effects.

End of May it was announced that US energy giant Chevron has won a major bid to explore for shale gas in northeast of Bulgaria.

Socialist MPs have now asked Bulgarian Minister of Economy and Energy Traicho Traikov to impose moratorium on shale gas drilling until further studies are conducted on the safety of the technique.

According to them, such an assessment must be commissioned by the Bulgarian Ministry of Environment, reports Bulgarian left-wing daily Duma Saturday.

Socialists have also asked for referenda among the local population in the exploration sites.

They have argued that not only production, but even exploration for shale gas might lead to severe damage to soils and underground waters.

Shale gas is a novel technique of producing natural gas that has boomed in the USA in the 2000s and up to now is largely unfamiliar in Europe.

It involves extracting gas dissolved in rock sediments known as shale, using a process known as hydraulic fracturing, during which water and various chemicals are injected at high pressures into the ground.

The process is recorded to have caused the escape of natural gas and other chemicals into the soil and water, causing damage.

The US Environmental Protection Agency is currently conducting a comprehensive survey of the technique and the need to regulate it more strictly, which is set to be concluded in 2012.