Well, you need a little energy to run the still, but I wouldn't worry too much about that. Burn wood if you're concerned about cost of that energy. But back to my main point: waste motor oil is free for very small amounts, but if you want a little more then it suddenly becomes impossible to find. So you're liable to build a whole infrastructure around something you can't get much of. I've done the math on every one of these pathways: vegetable oil diesel, synthetic fuel, algae, woodgas, methanol synthesis. Unless you're in one of a couple of very finicky areas like shipping, aviation, and large scale farming, nothing beats batteries.