North Sea oil
The Barnett formula, introduced in the late 1970s, had resulted in higher per-capita public spending in Scotland than England. If an allocation of North Sea oil revenue based on geography was included, Scotland also produced more per capita tax revenue than the UK average in the years immediately preceding the referendum. The Institute for Fiscal Studies reported in November 2012 that a geographic share of North Sea oil would more than cover the higher public spending, but warned that oil prices are volatile and that they are drawn from a finite resource. The Government Expenditure and Revenue Scotland report for 2012/13 found that North Sea oil revenue had fallen by 41.5% and that Scotland's public spending deficit had increased from £4.6 billion to £8.6 billion.