Its not just fuel but every other resource and commodity. We have seen recently how development of the likes of China and India have a huge impact on the supply and therefore the price of raw materials. We may indeed ultimately crack the problem of workable fusion power, but there are many other issues. Don't forget that oil supplies a lot more than petrol! Whilst there are many more untapped reserves than peak oil predicted they are in increasingly inaccessible areas or involve stripping the landscape in a way which may become ecologically and environmentally unacceptable.