ABERDEEN'S oilfield service companies could benefit from a massive expansion in the shale oil sector, according to accountant PricewaterhouseCoopers, but critics of the industry say the opportunity is overstated and the focus should be on the potential for green energy.

The shale gas and oil industry has expanded rapidly in the US, although controversy remains over fracking – releasing hydrocarbons by pumping water, chemicals and sand at high pressure to fracture the shale rock.

A PwC report published today predicts that, as production spreads, global shale oil output could reach 14 million barrels per day by 2035, or 12% of the world supply. The Scottish oil industry could benefit if shale deposits in central and southern Scotland are exploited and by lending expertise overseas. The UK economy could also be boosted by an energy price fall.

Alastair Geddes, a director in PwC's oil and gas team in Aberdeen, said: "Shale oil represents yet another exciting opportunity for the industry, particularly oilfield services companies. However, if we are to become a key international player in this market, a move that could positively impact investment, employment and economic growth across north east Scotland and the UK, then we need to grasp the opportunity."

In the UK, shale gas is being extracted in Lancashire after a temporary ban due to worries about earthquakes, and parts of Scotland are also thought to have shale reserves.

The Government will hold an onshore oil and gas licensing round this year which could result in more of the UK being opened up for exploration.

But Richard Dixon, director of Friends of the Earth Scotland, highlighted the uncertainty about how much shale oil and gas in the UK can be extracted and concerns that fracking can pollute water supplies.

The British Geological Survey estimated only 10%-20% of the UK shale gas reserve may be recoverable. Mr Dixon said the Scottish oil industry has large opportunities in catering to the renewable sector, notably wind power, and from decommissioning old North Sea oil fields.

He said: "There really is not any need to think about stuff that is difficult to extract and potentially contaminating.".

Kevin Forbes, chief executive of jobs portal Oilandgaspeople.com, said there has been little competition from the new energy industries for experienced North Sea employees but the oil industry is losing graduates to the renewables sector.

PWC estimates exploitation of shale oil could push global oil prices down by up to 40%. This would benefit oil importers and could add up to 5% to UK GDP.