For people in general, the most important consideration for different fuels is their relative performance and cost. This section aims to present some relevant information about how well the different fuel technologies compare in terms of energy capacity and cost.

*All estimates based on US Department of Energy figures for October 2006 and are in US dollars [1].

Octane number refers to the fuel's resistance to premature ignition. When fuel is injected into the combustion chamber of the engine, the piston begins to compress it. Premature ignition is when the fuel ignites from the compression before the sparks from the spark plug reach it. This can cause loss of power and damage to the engine. A fuel's octane number is measured relative to the explosiveness of a mixture of isoctane (2,2,4-trimethylpentane) and heptane. For example, an 87 octane rating of a fuel means that it is as resistant to combustion as a mixture of 87% isoctane and 13% heptane [2].

It is important to note that while compressed natural gas has a lower cost, it also has a much lower energy content per litre, meaning that while you may save money per unit of energy, you will have to fill your vehicle up nearly three times as often!  Currently, commercially available E85 gives you neither an advantage per unit energy, nor in the cost per unit energy, so not only will you have to refuel more often, you'll also have to pay more!  Vehicles using hydrogen fuel technology are so new and the market is so small that there are no prices available at the time these statistics were compiled.