Day change is also very important. For example, when you take an oil province 2h BEFORE day change (assuming its his only oil prov) you get 22/24 ~= 90% of his current oil stock. When you take it two hours AFTER day change, you only take 2/24 ~= 10% of his oil.
When he has a second oil prov of the same value, you only take 50% of those numbers for taking one of them, etc.
