Scotland's onshore deficit has consistently been more than 5% of GDP worse than the rest of the UK's
To illustrate the significance of fluctuating North Sea oil revenues, the chart below compares onshore deficits (i.e. excluding those North Sea revenues). This reveals the long-term underlying ~5% of GDP deficit gap that exists between Scotland and the rest of the UK. A corollary of this is that when Scotland's deficit has closed relative to the UK's, in the last 25 years this has always been because of surges in N Sea oil revenues.
As these insights explain, this onshore per capita deficit gap is mainly driven by higher public spending in Scotland, but lower onshore revenue generation is also a significant factor.