For years, FuelCell Energy has been considered a company to watch. Its technology promised to help economically reduce carbon dioxide emissions from power plants, which could help combat climate change. The Danbury, Conn., company might be able to make a difference, experts said, if only it had a partner with really deep pockets.

Now it has one.

In an agreement announced on Thursday, Exxon Mobil said it had tightened an existing relationship with FuelCell in hopes of taking the technology from the lab to the market.

Any commercial development is years away, warned Vijay Swarup, vice president for research and development at Exxon Mobil Research and Engineering. But, he added, “We think it’s got the possibility to be a game changer.”

Although the companies did not disclose the size of Exxon Mobil’s investment in FuelCell, “We’re putting the necessary resources behind this to take the research to the next level,” Dr. Swarup said.