The portion of the continental shelf which may be exploited is clearly laid down in international law. Around 92-95% of current known oil reserves lie in Scottish waters, and thus belong to Scotland. So, England would get between 5 and 8% of the oil.
The equidistant principal is only a starting point for negotiations. In international law, other factors are taken into account in order to give an “equitable” share of oil to each country. So, essentially because British resources have been used to develop the fields (e.g. HMRC have a specific division for oil and gas revenues) rUK could very easily argue that they should receive a greater share than the 5%-10% the SNP would be willing to agree to. These argument would stand up in the international court as international law often encourages parties to agree to an “equitable” conclusion
There is also a principal in international law which means maritime boundaries follow the land boundary. The current line boundary follows Berwick on Tweed in a north-easterly direction, not an east-west line that the SNP like to imagine. Project the current boundary into the North Sea and Scotland’s share drops closer to 60%. There are precedents in international law for this too.
The Shetland and Orkneys are believed to hold around 25%-30% of the UK’s oil. If they wished to stay in the UK they would take “their” oil with them, substantially deteriorating Scotland’s fiscal position.
There is no reason to believe these negotiations would be resolved quickly. The International Court took 4 years to decide on a row over boundaries between the Danish, Dutch and German parts of the North Sea.
Taken from Oil and Gas journal 2012.(tm)
Another complication here is the fact that the Orkney and Shetland islands have both indicated they would want to stay with the UK, if Scotland were to separate. These islands were seen as an extension of the UK mainland in UK-Norway negotiations about the borders for the North Sea, and so it is reasonable to assume the islands would have a similar effect if they wanted to stay with the UK, all be it they would be geographically located closer to a foreign country (Scotland).