Oil based economy?
1) Scotland's books are currently balanced (as legally required)
2) With 8.4% of the UK population, Scotland contributes 9.6% of UK tax revenue and receives only 9.3% of UK gov spending
3) Scotland currently contributes to vanity projects deemed to be 'National' (Trident, HS2, Crossrail, The Olympics (but oddly, the Commonwealth Games were 'local' and funded from Scotland alone)) that won't continue post independence
4) GDP/Capital *without* oil & gas is broadly similar (£20,873 -v- £20,571) between Scotland and rUK
it's no surprise that the economic case was that oil is just a Brucie Bonus: the Scottish economy can manage fine without it.
1) Oil was around $20/barrel for most of the 90s and it was still a welcome revenue to UK.gov
2) The oil companies are investing hugely: while of course the price is variable (which is why you build a sovereign wealth fund like every other oil producing nation except UK to buffer against it), the long term prognosis is still extremely healthy - £12m of investment announced just yesterday http://powerfromthenorth.blogspot.co.uk/2015/02/lerwick-harbour-defies-north-sea-gloom.html
3) In an era of ever increasing demand and finite supply, the price is only trending in one direction.
and finally, the kind of fear mongering lies told before the Referendum (e.g. Deutsche Bank who now say Scotland would be better off independent, or that the only way to save the NHS would be to vote No... how's that looking btw?) mean that it's hardly a surprise that many low information voters who unquestioningly rely on mass media (like yourself it would seem) got the wrong end of the economic stick.