Worst case scenarios of current estimates suggest that there is only about 40 years supply of fossil-based fuels left. That means the search for alternatives is of growing importance.
And it's not just the fuel that matters. With continuing concerns about greenhouse gas emissions, the search for environmentally-friendly energy sources is a top priority.
Bio-fuels produced from plants will play an increasingly important role and DaimlerChrysler has been researching plants that could yield low-emission, high- quality fuel. Diesel is favoured because the oils produced from plants deliver more potential diesel than petrol.
The most recent research project is based in India, where the Jatropha plant grows wild in many parts of the country.
Cultivation needs are low because the plant will grow in poor soil. The plant produces large quantities of seeds, consisting of about 60% oil, which can be turned into diesel.
The resulting fuel has a high cetane number. This measures how readily the fuel starts to burn, roughly equivalent to octane for petrol with the higher the cetane number the better the fuel.
Jatropha diesel is also low in sulphur, while the waste product from making the fuel is a good natural fertiliser. DaimlerChrysler is cultivating two test plantations in partnership with others.
The company believes that such fuels will form part of the wider family of synthetic diesels, which can be produced from a wide range of sources including waste wood, straw, and methane gas, as well as crops.
In partnership with Volkswagen and Choren Industries of Germany, DaimlerChrysler has been involved in small-scale production of synthetic diesel, tagged Sun Diesel, produced from waste wood.
The result is a high-quality fuel with a cetane number of about 75-80 compared with 50-55 for conventional diesel. Sun Diesel is also free of sulphur and aromatics, reducing particulate emissions by about 15%.
It's also termed carbon dioxide neutral because the carbon dioxide emitted by an engine is equivalent to that absorbed by the plants used to produce the fuel. DaimlerChrysler believes that synthetic diesel could account for about 20% of European needs.
Since it is a synthetic fuel it can be used pure in any diesel engine. Biodiesel has to be blended with conventional diesel to a maximum of 5% in most cars, because it attacks seals in the fuel system.
Currently, only Volkswagen Group diesels are designed to run on 100% biodiesel. The drawback is that at today's prices, Sun Diesel costs three to four times as much as conventional diesel to produce.
High cetane fuels make diesels quieter than normal and a 150bhp E220 ran very smoothly on Sun Diesel when put through its paces at the Mercedes-Benz Stuttgart test track. The high-quality fuel meant there was no loss in performance either. In fact it was impossible to tell the car apart from one running on conventional fuel.
The only difference is in the smell of the fuel, which is slightly sweeter than forecourt diesel. If oil prices continue to rise, we could find ourselves driving synthetic diesel powered cars sooner than we think.