For heavy-duty vehicles and road transportation, fuel consumption and associated CO2 emissions have been of great concern, which has led to the development and implementation of technologies to reduce their impact on the environment. Low viscosity engine oils have arisen as one proven cost-effective solution to increase the engine efficiency; however, for the heavy-duty vehicle segment, engine protection against wear is a priority for end-users, and therefore there is some reluctance to the use of that new oil formulations. In this study, eight lubricant oils, representative of the HTHS viscosity reduction that heavy-duty oils have been undergoing and new API CK-4 and FA-4 categories, were evaluated for fuel economy, oil performance and engine wear, in a long-term test involving a fleet of 49 heavy-duty vehicles of four different engine technologies, some of them with diesel fuel and others with compressed natural gas. Results of fuel economy were positive for most of the buses’ models. Regarding oil performance and wear, most of the formulations were found to be suitable for extended oil drain intervals (ODI); and although no alarming results were found, overall performance of the formulations of the fourth stage could lead to significant wear if the oil drain interval is extended. In this study, it should be noted that some of the information has been presented by the authors in other publications, here they are presented with the purpose of complementing the new results and summarize the entire test.