The previous post was very strong. I would say that there is a difference between what is working now and what might not work in the future. I think that there is a concession the petrol is the most viable source right now. However, I think that this does not mean that exploration of other sources of fuel should be stopped or should be regressed. There are many problems with being dependent on foreign oil. These can be fully sources through research online or through scholarly articles. The most elemental challenge though is that crude oil used for petrol is not finite. It can and will run out. The growth of economies all over the world and the greater competition for oil will cause it to disappear. If nations are so dependent on it and refuse to investigate other sources of energy, the implications are grave when it expires. I think that while there is a natural state of dependence on petrol and oil, investment in alternative technologies have to be present in order to prevent a dreadful reality of what happens when the supply expires with nothing to substantiate it.
Petroleum products are the most viable sources of fuel for motor vehicles at the present time because of their availability and the current technology for extracting and processing them into usable products. The necessary infrastructures are in place and have been for decades. A few other technologies and products are in the marketplace but have not received widespread acceptance for various reasons namely the expense of changing the infrastructure to enable mass production.
As far as future technologies and products go, you will undoubtedly receive very spirited opinions as to which technologies and products are most viable. Several are on the horizon but as of yet, they are not feasibly mass produced. Many remain in infancy stages of design and production.