The energy demands and rising cost of oil have encouraged scientists and engineers to develop renewable energy alternatives. Biofuels are renewable energy sources from organic materials such as plants or animals that are directly converted into liquid fuels. The two most common biofuels in use today are ethanol and biodiesel. Engineered biofuels, such as ethanol and biodiesel that are made from starches, sugars and cellulose are already in use as blending agents and additives that greatly reduce vehicle emissions. Algae as a bio-fuel has become more common because it is easy to harvest and these single celled photosynthetic organisms are known for their rapid growth and high energy content.