The current Swift offering is petroleum-based but the original Swift fuel was biomass based (sweet sorghum as I remember), and when tested to the same standards as the existing 100LL, it met or exceeded all the different parameters. Years ago our local builder's group participated in a video conference with the Swift people and this is what I remember about it. We also saw a photo of the engine instrumentation of a Beech Duke being flown on Swift fuel on one engine. Power was set the same but the Swift-fueled engine ran cooler and had a lower fuel flow.
I asked the Swift people about the biomass fuel at Oshkosh and they told me it had been funded by private interests who later withdrew their support.