This report for the AB 118 Project entitled "Late Stage Development, Demonstration and Product Launch of Cummins Westport 11.9 Liter Natural Gas Engine" was funded under Energy Commission Grant ARV-09-013. Work under this grant commenced upon the completion of work performed under CEC Agreement PIR-08-044 from the Energy Commission’s Research Division. PIR-08-044 supported ISX11.9 G engine concept development and creation of the "alpha" design. This report includes completion of the engine build-out, validation testing, emissions certification, demonstration tests, and manufacturing readiness tasks leading to commercial launch of a new low emission, high performance natural gas 11.9 liter engine for the heavy-duty Class 8 truck market.