Peterbilt says it will offer the natural gas Cummins Westport ISX12 G engine when it becomes available in 2013.

This engine will be rated up to 400 horsepower and 1,450 pounds-feet of torque. It features spark ignition technology, a three-way catalyst, and can be configured with a liquified natural gas or compressed natural gas fuel system.

Peterbilt has offered trucks featuring liquefied natural gas (LNG) and compressed natural gas (CNG) fuel systems since 1996. Peterbilt currently offers two natural gas engine platforms:

- The Cummins Westport 8.9 liter ISL G with 320 horsepower at 1,000 pounds-feet of torque features spark ignition, and a three-way catalyst emission system that can be configured with either LNG or CNG fuel systems.

- The Westport HD 15-liter engine with 475 horsepower and 1,750 pounds-feet of torque uses diesel pilot ignition, which is configured for the LNG fuel system only.