The Scots economy is not wholly dependent on oil. And don't forget it's a small country of only around 7 million people. An independent Scots economy is certainly viable.
Of course the Scots economy is not wholly dependant upon oil. The North Sea oil industry is declining rapidly and within the next 5-15 years will become a liability as the astronomical costs of decom overtake revenues.
Is an independent Scotland viable?
It's impossible to say as it depends on too many unknowns such as the nature of the independence, the reactions of other countries, businesses and other stakeholders and it also depends what you mean by "viable".
What would be the response of buyers of Scots exports? At the moment Scotland almost exactly breaks even in terms of it's net contribution to UK GDP, would it continue to break even as a smaller trading unit with higher costs?
Would Scotland be in the EU? Would they want it? Would the EU accept them? If so would Scotland receive any subsidies from the EU and how much would they be worth?
Would Scotland be part of the euro?
What about transport links and infrastructure? At the moment a large proportion of Scottish exports travel by road to English ports, would that continue? Would tariffs be imposed?
Would Scotland be part of NATO? How much would it's contribution be and at what cost?
On the question of "viability". At what standard of living do you have in mind? The same as now? Lower? Higher? I know it's not a perfect comparison and times have changed, but Irish independence plunged that country into third world status for half a century. Still "viable" though.
Incidentally Scotland is much smaller than you think.
The estimated population of Scotland was 5,222,100 in mid-2010. This was a rise of 28,100 on the previous year and the highest population since 1977.http://www.scotland.gov.uk/News/Release ... 4/27095112
I'm not saying it won't work and I'm certainly not Scotland bashing.
I'm not even saying that it shouldn't
I'm cautioning against making sweeping statements based on unknowns.