This thesis describes a usability study designed to increase an automotive designer's understanding of how to design effective dual-fuel gauges for hybrid vehicles. Hybrid Electric Vehicles (HEVs) aim at reducing dependency on gasoline. While gasoline has one primary source, which is non-renewable, electricity comes from renewable as well as non-renewable sources of energy. As we begin to generate electricity more efficiently from newer power plants that are built using renewable energy, it is important that drivers of HEVs begin to reduce their dependency on gasoline and rely more on electricity for operating their vehicles. Hybrid fuel gauges have a role to play in the overall user experience and adoption of HEVs. When purchasing a car, people take into consideration how the instrument panel looks and how understandable it is (Green, 1984). Therefore, it is important that these gauges are effective in providing information on fuel levels so that it can be read quickly and accurately.The goal of this work was to identify a class of gauges that support quick and accurate reading so that the driver can understand when to recharge the electric battery or refill the gas tank for efficient trip planning. A set of thirty-three hybrid gauge designs created by designers at General Motors was provided to the University of Minnesota team. The UMN team created four new gauge designs that were different from the ones created by the General Motors. These were reduced to a set of nine gauges by the process of heuristic evaluation. A two-part usability study was conducted with sixty drivers. In the first part, drivers participated in a timed comprehension task in which they were made to view certain gauges and answer questions on them. This was followed by a subjective questionnaire in which participants were asked about their preferences for various gauges.Vertically oriented bar gauges were found to be most effective. They elicited the highest accuracy rates and lowest response times compared to horizontally oriented bar gauges and circular gauges. Participants were able to process information in relative form (expressed in graphical or pictorial form) more easily and accurately than information in absolute form (expressed in numeric form). Familiar types of gauges, which appeal to participants, do not always contribute to better performance. Introducing new types of gauges requires more upfront marketing of their benefits (such as higher reading accuracy and speed).A set of recommendations has been created for automotive designers on how to create effective hybrid fuel gauges. These recommendations are important in driving standardization of hybrid fuel gauges to help deliver a consistent user experience and to minimize confusion and user frustration. These gauges encourage fuel-efficient behavior by helping drivers reduce their dependency on gasoline, thereby reducing pollution from carbon dioxide emissions and ultimately resulting in a cleaner environment.