Is petrol the most viable source of fuel for motor vehicles at this time and in the future?

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.