Going green is taking many forms, and cruise lines are now working on harnessing a fuel that’s lighter than air.

Hydrogen fuel cells are in the long-term thinking of both Royal Caribbean Cruise Line and Viking Ocean Cruises as a way to eliminate the emissions from burning hydrocarbon fuels.

Viking announced early work on a project for “what could become the world’s first cruise ship with zero-emission technology” at the annual Safety at Sea conference in Haugesund, Norway. Viking’s project manager Serge Fossati said that while liquid hydrogen is not currently produced on a large scale in Europe, the company is in discussions with Statoil, Norway’s government-owned energy company, about how production could be significantly expanded.

One of the drawbacks of fuel cells is that the standard process of producing hydrogen from oil or gas using conventional gas generators can create more greenhouse gases than are saved by using the hydrogen for power.

But Norway has an abundance of electrical power from hydro-electric power dams that don’t create emissions. That means that Norway could take the lead in a new era of fuel cell ships using hydrogen split from water by electrolysis that doesn’t create emissions.

It’s all still at the theoretical stage and at the moment, Viking doesn’t have a ship on the drawing boards to be the pioneer of the new technology. “The road to that point is still long,” Viking chairman Torstein Hagen admitsted in a statement. “But here at Viking we want to be ahead of the game.”

However, Royal Caribbean is working on a fuel cell power system for a new “Icon” class of ships being developed for 2022 and after. Actual propulsion is still likely to be fueled mainly by liquefied natural gas.

The concept of fuel cells has been around for a century, but practicality of keeping the hydrogen in storage and limited production has kept them impractical for large-scale use in transportation.

But a lot of research is going on to make them more efficient and it’s a promising sign that cruise lines are taking efforts to be at the forefront of the effort to make them a practical green alternative to oil.