It's not the yield, but the profit.
Statoil makes huge margins on their oil because once the tricky rig was set up, it just comes out like Gold.
Most other natural resources have much thinner margins due to processing, overhead.
'Sweet Crude' i.e. the kind you get in the desert, and 'sweet once it's setup to be' i.e. Statoil ... this is a different thing together from other natural resources.
Norway is like Kuwait, it's almost impossible to compare it to anything else.
They can leave the Oil in the ground for now because they are very rich and have more money than they know what to do with.