Westport Fuel Systems Inc (WPRT)

[pack10]

This is the first indication I've come across that gives a hint as to the number of NatGas units in service.
seems like a pretty good number as they are relatively recently introduced engines.

Based on the ISL G and ISB6.7 G natural gas engines, the 2018 L9N and B6.7N build on the experience gained from over 80,000 Cummins Westport engines currently in service and provide a present-day solution to urban air quality issues. In addition to ultra low emissions, the L9N and B6.7N feature a new engine control module with improved durability, on-board diagnostic (“OBD”) capability, an enhanced maintenance-free three-way catalyst, and a closed crankcase ventilation system.