Oil
The main criteria of a car's eco-friendliness is generally seen as the
energy it uses in its operation. Cars have primarily run on oil-based
fuel in the form of petrol or diesel for over a century. But we are
now at the point where demand for oil is rising so much, and reserves
are declining, that oil is actually running out. Oil prices have
always been volatile and they react to speculation about events
ranging from terrorism to hurricanes, but rising demand and
diminishing reserves mean that overall, oil is just going to keep on
getting more expensive. However despite this, most cars today still
rely on oil as their primary source of energy; and oil is obviously a
key contributor to carbon emissions, and climate change.
Petrol
Petrol has been the most popular fuel for cars in the UK for years;
petrol engines are generally quiet and smooth, they are responsive and
their performance is good. Petrol is currently slightly cheaper than
diesel. Petrol engines emit around 10% more carbon dioxide (CO2) than
diesel. However petrol cars pump out less toxic emissions than diesel.
Unfortunately at the moment there is no single source of fuel which
can compare with petroleum in terms of its instant bulk availability,
energy density and (relative) cheapness....

http://groups.google.com/group/waterforfueld