Various international literature sources and papers address the issue of the theoretical implementation of using liquefied petroleum gas (LPG) gas as catalyst material injected into the carburetor system of diesel engines and its positive impact on the characteristic features of the engine and its emission. In Europe, for example, Landi-Renzo, one of the biggest Italian companies dealing with traditional gas systems, is developing a compressed natural gas (CNG)-diesel system. The present paper outlines the operational characteristics of a diesel-LPG dual operating system based on our own experiments and measurements which have been carried out on the transformed buses of the Southern Transdanubian Transportation Centre (DDKK, Hungary). In the process of evaluation two aspects were taken into consideration: the impact on emission and that on fuel consumption. Of course, the tests can be extended to wider areas, which take into account both vehicle structures and the environment (Palkovics and El-Gindy, 1993; Palkovics et al., 1996; Shokouhfar et al., 2016).