A 75-gallon tank of goo that in the course of a week or so changed color from lime green to almost black was one of the stars of last summer's Farnborough International Air Show in England.

As airlines ordered hundreds of planes worth billions of dollars at the world's largest air show, the tank, or bioreactor, was a near-perfect breeding ground for what could become the fuel of the future: the lowly algae.

Aerospace companies and airlines are betting that algae — simple organisms that come in some 30,000 species, many of which can be genetically modified — will prove to be a green fuel that can power jet planes. Algae also could be blended into diesel and gasoline, and perhaps could even replace petroleum-based diesel and gasoline one day.

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