EcoRouting refers to the determination of a route that minimizes vehicle energy consumption compared to traditional routing methods, which usually attempt to minimize travel time. EcoRoutes typically increase travel time and in some cases this increase is constrained for a viable route. While significant research on EcoRouting exists for conventional vehicles, incorporating the novel aspects of plug-in hybrids opens new areas to be explored. A prototype EcoRouting system has been developed on the MATLAB platform that takes in map information and converts it to a graph of nodes containing route information such as speed and grade. Various routes between the origin and destination of the vehicle are selected and the total energy consumption and travel time for each route are estimated using a vehicle model. The route with the minimum energy consumption will be selected as the EcoRoute unless there is a significant difference between the minimum time route and the EcoRoute. In this case, selecting a sub-optimal route as the EcoRoute will increase the probability that the driver uses a lower fuel consumption route. EcoRouting has the potential to increase the fuel efficiency for powertrains designed mainly for performance, and we examine the sensitivity of the increased efficiency to various vehicle and terrain features. The reduction in energy consumption can be achieved independent of powertrain modifications and can be scaled using publicly available parameters. / Master of Science / The automotive industry faces increasingly strict government regulations and standards for fuel economy while maintaining the safety, performance, and consumer appeal of the vehicle. Hybrid Vehicles are cars that run on a combination of fuel an electricity. Plug-In hybrid vehicles are a subset of hybrid vehicles that have a large battery pack that can be charged externally. These vehicles therefore are a relatively cleaner form of energy and provide more mileage for the same amount of fuel. It is however important to consider the source of electricity generation when evaluating the environmental impact. Though hybrid vehicles typically have better fuel economy than their conventional counterparts, further improvements can be made on total energy consumption. EcoRouting is a step towards achieving the high standards set for a sustainable future. EcoRouting refers to a fuel efficient route that is still a viable alternative over the shortest Travel Time (TT) route, typically selected by routing applications and users alike. The major goal of the EcoRouting module developed here is to find a fuel efficient route which still has a viable travel time for it to be considered by the user. Maintaining a balance between the commute time and fuel consumption of the vehicle is key to ensure that drivers actually select EcoRoutes to fulfill their commuting requirements. This thesis lays out a method considering traffic conditions and the way the vehicle is driven. This method is be applied to applied to road networks in Detroit and San Francisco to gather extensive quantitative data. The data is used to analyze scenarios in which taking an EcoRoute will actually be a viable alternative for drivers of plug-in hybrids. The results show that EcoRouting is definitely viable for PlugIn hybrids and it depends highly on driver behavior and their priority of commute time. Furthermore, EcoRouting for PHEVs is more suited to city driving compared to highway driving. The EcoRoute varies and needs to be customized to the driving style of the user.