Argentina is the world´s biggest user of CNG for cars. Obviously that has led any amount of gasoline engined forklift truck users to convert to CNG/gasoline. Any gasoline engine can be converted at low cost, but CNG burns hotter and many engines, specially the ones with aluminium block and heads end up with burned out valves and valve sleeves sinking any where up to 3 mm into the aluminium block. That whipes out any possible savings or low poilution advantage.