As affordable petroleum becomes scarcer, it’s easy to imagine switching to electric cars or outfitting hydrogen-powered ships with supplementary sails. But it’s harder to picture what we might run jumbo jets on in the future. Perhaps passengers will help to drive propellers as whip-wielding stewardesses urge them to pedal faster, or reach under their seats to hook fresh batteries to electric engines in mid-flight. This hardly seems likely, though. So what might really keep air travel viable in a post-petroleum world?

One of the main candidates is butanol, a close chemical relative of the fuel in butane cigarette lighters. It’s more suitable for aviation than ethanol, which offers only modest energy outputs, isn’t fully compatible with existing internal combustion engines, and corrodes the pipelines it travels through. Butanol is made from the fibrous cellulose in pulverized wood, which is fed to yeasts that digest it into a flammable liquid that yields more energy per gallon than ethanol does, works better in standard engines, and doesn’t eat its own transport pipes.

As with most emerging technologies, it’s not yet economically viable in comparison to gasoline (for cars) or kerosene (for jets). But that’s not saying much. In the coming decades, gasoline and kerosene will become less affordable as petroleum sources dwindle, and $100-a-barrel oil has already made alternative fuels more competitive than they were a few years ago. With that in mind, inventors and investors are developing biobutanol as a possible savior for the airline industry.

In central Maine, for instance, a fiber and fuel mill is setting its sights on butanol production.

The goal is to sell pulp to paper mills at first, but eventually the company hopes to send most of its ground-up trees to fermentation tanks.

If all goes according to plan, biobutanol operations such as this could give a much-needed boost to Maine’s struggling timber industry.