A case study was conducted in a CNG engine powered urban transport fleet to monitor and analyze oil condition required to generate maintenance savings. The case study used a real urban transport fleet, which used diesel and CNG powered vehicles, to quantify the differences in the engine oil degradation rate for the two types of engine and to assess how different cost or quality engine oils behaved in CNG vehicles. A comparative assessment of engine oil behavior between diesel and CNG engine powered vehicles was performed, showing that demands on CNG engine oils were higher than in diesel engines, as highlighted by a faster oil degradation rate in the earlier engine. An urban transport fleet company agreed to collaborate with the case study to realize these objectives. Two different vehicle types were considered for the investigations, such as CNG and diesel engine powered vehicles.