Airlines will need all of the world’s synthetic aviation fuel, meaning there won’t be any left for cars, the head of Europe’s biggest airline group told Germany’s automakers.

Deutsche Lufthansa AG Chief Executive Officer Carsten Spohr said so-called sustainable aviation fuels offer the only workable path to decarbonizing air travel, though supplies are tight.

“With no technology in sight to replace fuels, we really need all the sustainable aviation fuel in the world,” Spohr said at Germany’s biggest auto industry gathering in Munich. “Oliver can maybe have some for his 911, but we really need the volumes,” Spohr said, referring to Porsche AG CEO Oliver Blume’s push to get exemptions from combustion engine bans.

Germany’s automotive sector, which employs about 800,000 workers in Europe’s biggest economy, has successfully lobbied for an exemption for e-fuels from the European Union’s 2035 combustion engine ban. As a result, the ban will not cover cars run exclusively on the liquid fuels that are made by combining hydrogen and carbon dioxide that was already in the atmosphere.

So-called SAF is seen by aviation executives like Spohr as the only viable way to decarbonize air travel. While battery-electric vehicles work for road travel, cells lack the energy density for the foreseeable future to lift a commercial planeload of passengers and cargo into the sky.