Rentech "rents" technology that turns carbon-bearing gases, liquids, and solids into products useful for carbon-based life forms -- humans. Its technology -- called the Rentech Process, its own variation on the Fischer-Tropsch (FT) process -- is licensed to third-party plants for converting biomass, waste, and fossil resources into synthesis gas (syngas) and then into hydrocarbons to be refined into products like diesel fuel, jet fuel, and specialty waxes. Of course, it doesn't make much money doing this. That's why Rentech bought Royster-Clark. That company's nitrogen products business now makes up the bulk of Rentech's money-making operations, providing funding for its Rentech Process development.