A study has found "little prospect" that any financial surplus would be available for a potential oil fund in an independent Scotland.

The Centre for Public Policies for Regions (CPPR) looked into the viability of the Norwegian-style scheme, which First Minister Alex Salmond hopes to establish if Scotland gains full control of tax and finances.

While the fund is possible, the report also suggests "very difficult decisions" will need to be taken.

The report adds: "At existing oil prices and production levels, all North Sea taxes are, and will continue to be, needed to help fund the deficit that emerges from maintaining existing levels of public services.

"There is little prospect of any surplus becoming available for an oil fund, and certainly not of the size being suggested."

Mr Salmond, in a speech to the London School of Economics on February 15, said that £1bn a year, invested over 20 years, would create a fund for Scotland worth just under £30bn.

The CPPR said the annual real return, or yield, would need to be at least 4% a year and no money could be spent from the fund in the 20 years to reach the target.

Jo Armstrong, one of the report authors, said: "Investing £1bn each year in an oil fund will add to the Scottish Government's budget challenges.

"With current oil prices and more importantly, with declining North Sea production, such a level of investment will put current service levels at risk or will require adding to Scotland's debt levels."

Director of CPPR Richard Harris said: "Whilst the inter-generational equity arguments for a fund may appear strong, it is by no means clear that establishing a fund and releasing funds in 20-years time will necessarily be the best approach for Scotland's economy and its future generations."

A Scottish Government spokesman said Government Expenditure and Revenue Scotland (GERS) figures show that from 2005 to 2010 Scotland was in a stronger financial position relative to the UK as a whole by a total of £7.2bn.

The spokesman added: "Taking all spending in Scotland into account and all of our revenues, Scotland has run a current budget surplus in four of the five years to 2009-10 - while the UK was in current budget deficit in each of these years, and hasn't run a current budget surplus since 2001-02."

But Scottish Labour finance spokesman Ken Macintosh said: "If Scotland started an oil fund in the same year as Norway, the current balance would be zero because we spend more on public services than raise in tax.

"This debate is about the choices governments make. Norway has chosen to put money in a bank account; Scotland has chosen to invest in public services.

"If Alex Salmond wants to change that, he needs to spell out what further cuts he is proposing because you can't spend the same money twice.

"The SNP's argument about what did and didn't happen 30 years ago doesn't speak to the reality of the choice today.

"Basing our entire economy on a single commodity that is volatile in price and finite in supply is a risk that we avoid by working in partnership with the other countries of the UK."