It took more than 200 million years to form all of the oil beneath the surface of the earth. It has taken 200 years to consume half that endowment. If current rates of consumption were to continue, the world's remaining resources of conventional oil would be used up in 40 years.

But that would not be the end of fossil fuels. The world's coal resources are much larger, and there are vast amounts of unconventional fossil fuels, such as shale oil, tar sands, and natural gas trapped in ice beneath the ocean. At present, these energy resources are too expensive to use, and would produce much greater harm to the environment.

In the future, ways may be found to use some or all of these resources economically and without undue damage to the environment. Advanced technologies may be developed to produce clean, economical energy from other sources.

In the meantime, it makes sense to use fossil resources such as oil more efficiently to reduce environmental impacts and buy time to develop new and better energy sources.

Two-thirds of the oil we consume powers transportation vehicles, and half goes to passenger cars and light trucks. Being a fuel-economy conscious consumer doesn't mean buying a car you don't want. It means shopping around to find a vehicle that gives you all the features you want with the best fuel economy available. This will not only help conserve fuel today, but will signal carmakers to use advanced technology to make cars even more energy efficient in the future.