an alternative-fuel version of the saab 99 gl called the "petro" was developed by the joint venture saab-valmet and built at the valmet factory in uusikaupunki. this model had dual fuel tanks - one for petrol and one for either kerosene or turpentine, the latter being produced from paper-mill byproducts in finland, the only market where the car was sold. the engine was started on petrol, then automatically switched to the other fuel, although the driver could select petrol only with a manual override switch. low-compression pistons from the turbo were used in this version of the engine, as was the electronic ignition. the petro first appeared in 1980. running on 67 octane kerosene the engine produced at 5600 rpm. 3,756 saab 99 gl petros were built.