Three diesel tractors, converted to compressed natural gas (CNG), have been demonstrated on Saskatchewan farms. This paper presents the results of laboratory and field monitoring over a two year period. Dual-fuel conversion systems were installed on a John Deere 14440 tractor and on a White 2-180 tractor powered by a Caterpillar 3208 engine. A Deutz-Allis 7110 tractor came equipped to run on 100% CNG. The conversion system in the John Deere was mechanical with solid-state controls, the system in the White was microprocessor controlled, and the Deutz-Allis was equipped with spark ignition and a natural gas mixer. In addition, sufficient storage was installed on each tractor for field work over a 12-hour day. Performance results are presented for each tractor, including hours of operation, power output, thermal efficiency, percentage CNG substitution and fuel consumption. Problems encountered in the field are also discussed.