Opal Fuels LLC, with a growing portfolio of nationwide renewable natural gas (RNG) and landfill projects, is going public in a combination with an affiliate of energy infrastructure giant ArcLight Capital Partners LLC. 

The definitive agreement announced Thursday would launch Opal, a Fortistar portfolio company, on Nasdaq under the ticker “OPL.” Co-CEOs Adam Comora and Jonathan Maurer would continue to lead Opal, with backing from ArcLight Clean Transition Corp. II, a special purpose acquisition company.

“This transaction with ArcLight reflects a transformative step in our company’s development and strategy,” Comora said during a conference call with investors. “RNG-powered heavy duty fleets realize substantial savings today versus diesel, and the successful...