@KanaMauna apparently.

The petrol companies kept the price of diesel low enough to make it uneconomical to produce bio-diesel, unless the vegetable oil was free for the taking from a used source. And even then the bio-diesel companies were mostly kept in business by government mandates - my state mandates 10% of diesel at the pump must be bio-diesel.

Online sources claim bio-diesel production cannot scale fast enough to cash in, and future demand is too uncertain to invest in infrastructure.