Jason Torchinsky of Jalopnik says yes. He takes a look at the two products produced by butts: flatus and feces, and determines the harvestable energy in each. The good news is that butt fracking is a group building exercise: "It would take you months and months to fill an 8 gasoline gallon equivalent (GGE) tank like the one in the Honda Civic CNG. Oh, and remember, of that 100 ml fart, only 30% of that (at best) is methane — so to do this right, you'd want to pool a whole community of farts. It's really the only way."
Will Jason's article usher in a resurgence in gas bag cars?