Analysis: Why is there petrol scarcity?

For weeks (in some places for months), there has been a scarcity of petrol across the country. The scarcity has heralded long queues at filling stations, and many stations are selling at prices that are way higher than the official pump price per litre. In many parts of the country, petrol is sold for as high as N250 per litre as opposed to the official rate of N165.