Houston, the fourth largest metropolis in the US, currently experiences severe air pollution. Major pollutants, such as VOCs, CO, NOx, PM, SOx, CH4, and CO2, are released from the transportation fleets. To decrease fossil fuel use and greenhouse gas emissions from fleet vehicles, more and more biodiesel is used in vehicles in the Houston metropolis. The GREET model was used for simulating the fuel cycle emissions of diesel vehicles using different biodiesel blends in Houston. The fuels examined were diesel-biodiesel blends of B0, B5, B20, B50, B80, and B100. The energy and water use and emissions from vehicles fueled with the blends were investigated. The study shows that the reductions in GHG emissions are significant at the Well-to-Pump stage, and all the emissions, except GHGs and NOx, reduce at the Pump-to-Wheel stage. The overall Well-to-Wheel analysis shows that biodiesel is beneficial for both passenger cars and heavy duty trucks. However, the benefits are more pronounced for passenger cars compared to heavy duty vehicles. When 50% of diesel passenger cars and HDDTs are switched to B20 in the Greater Houston area in 2025, the daily GHG emissions will be reduced by 2.0 and 712.1 CO2-equivalent tonnes, respectively.