Scottish independence: Tories claim oil estimates were wrong
The Conservatives have accused the Scottish government of getting its projections on oil and gas revenues "spectacularly wrong".
Newly-published statistics showed Scotland's share of North Sea revenue was £4bn in the financial year 2013/14.
The Tories said the Scottish government had last year predicted income for 2013/14 could be between £7.1bn and £8.3bn.
The Scottish government disputed the Conservatives' claims.
Conservative MSPs raised the figures with Energy Minister Fergus Ewing during exchanges at Holyrood.
The party's finance spokesman Gavin Brown said: "Oil and gas figures published this morning by the Scottish government show that they collected £4bn in the financial year 2013-14. That's down from £5.5bn in 2012-13.
"The Scottish government said we were going to collect between £7-8bn for 2013-14.
"Can the minister explain why the Scottish government got it so spectacularly wrong for the second year in a row?"
Mr Ewing responded: "The oil price this morning was $103 (£61.60) a barrel. That figure is extremely satisfactory and there is nobody in the industry apart from Mr Brown that anticipates that oil will be anything other than an enormous advantage, rather than a problem as Mr Brown seems to think."
The energy minister said production of oil and gas in Scotland would increase "massively" as a result of new fields such as BP Clair and Statoil's Mariner opening up, ensuring "enormous wealth and opportunities" for Scotland.
He said: "What a shame it is that on every occasion the Tories and their Labour friends talk down this industry, deterring young people from seeking the enormous opportunities that there are."
He was pressed again on the issue by Conservative MSP Murdo Fraser, who called on him to explain why the figure was "precisely one half of the estimated figure from the Scottish government".
Mr Ewing said he disputed Mr Fraser's "mathematics and conclusions".
"It's clear that the enormous oil wealth over the next decades will be a massive advantage provided the right decisions are taken, and sadly the wrong decisions have been taken over the last 40 years," he said.
The newly-published quarterly national accounts showed North Sea revenue totalled £964m in the first three months of 2014.
When combined with the figures from the previous three quarters, the total for 2013-14 was £4.005bn.
A spokeswoman for the Scottish government later said the figures were "entirely consistent" with the its Oil and Gas Analytical Bulletin published in May this year, in which it lowered its estimates of the country's oil and gas tax revenues over the next five years.
She added: "The bulletin made clear that record levels of investment in the North Sea will reduce revenues in the short term - however it also highlighted that this investment will allow new fields to come on stream and in turn increase production and revenues.
"It is estimated that the investment in the industry will see production increase by 14% between 2013 and 2018. If production and investment trends follow the industry's own latest forecasts and oil prices remain at $110, Scottish receipts could increase to around £7bn a year."
But Scottish Liberal Democrat leader Willie Rennie said: "These new figures confirm that oil revenues are volatile, uncertain and falling.
"What makes matters worse is that an independent Scotland would be over dependent on this resource, posing a real threat to our public services like the NHS.
"The Nationalist government has been desperate to inflate the value of oil in the run up to the referendum in a desperate bid to inflate their chances of victory, but have now been found out."