Airplanes Flying on Algae Scum

Choice quote:

Boeing has stated publicly since then that it believes algae is the airline fuel of the future.

Goes something like this: algae grow through normal photosynthesis (which captures CO2) using only the free and abundant sun light, algae get collected and processed, algae is turned into some sort of biofuel (like ethanol), and said biofuel is put on planes. Result is 0% emissions of greenhouse gases from airplanes. Not bad, but I'm curious to see what Exxon and Shell have to say about this. Article here.