Earth scientists believe the world has about 40 years worth of oil still buried in its rocks—but they've been saying the same thing now for at least... 40 years! Whatever the reality about "peak oil", one thing is certain: with ever-growing numbers of vehicles on our streets, oil is going to become more expensive and harder to obtain over the next few decades. That's why many people think the future lies with alternative fuels made from crops and waste products. Known as biofuels, these potentially offer many advantages over petroleum. They could help us tackle global warming and, by reducing our dependence on oil from the Middle East, they could help make the world a safer place. But biofuels have major drawbacks too. Critics think their environmental benefits are overstated and argue that, by taking land that would otherwise be used for growing food, they could severely worsen poverty and hunger in developing countries. Let's take a closer look at how biofuels work and consider some of the pros and cons.