Oil-rich states like Oman can afford to subsidise the price of petrol to below market rates. I can't say I really like it because it encourages very wasteful use of fuel.
Also, about 60% of what we pay for petrol is tax, designed to reduce consumption and discourage imports. This is down significantly from 1997 when 81.5% of what we paid for petrol was tax. Since the cancellation of the fuel duty escalator in 2000 the percentage paid in tax has steadily decreased.