- [Fuel Economy and Environment](https://www.fueleconomy.gov/feg/hybrid_fe_tech.shtml)
- [Hybrid Electric Vehicle Technology](https://www.energy.gov/eere/vehicles/articles/hybrid-electric-vehicle-technology)
2. U.S. Environmental Protection Agency (EPA):
- [Fuel Economy Guide for Hybrid and Electric Cars](https://www.fueleconomy.gov/feg/hybrid_electric_car_guide.shtml)
- [Green Vehicle Guide](https://www.epa.gov/greenvehicles/)
3. California Air Resources Board (CARB):
- [Hybrid Electric Vehicles](https://ww2.arb.ca.gov/our-work/programs/hybrid-and-zero-emission-vehicle-program)
4. International Council on Clean Transportation (ICCT):
- [Hybrid Vehicles & Emissions](https://theicct.org/publications/hybrid-vehicles-emissions)
5. HybridCars.com:
- [Fuel Efficiency and Emissions](https://www.hybridcars.com/fuel-efficiency/)
6. Plug-In America:
- [Hybrid Electric Vehicles (HEVs) vs. Plug-In Electric Vehicles (PEVs)](https://www.pluginamerica.org/learning-center/alternative-vehicles/hybrid-electric-vs-plug-in-electric-vehicles/)
7. Green Car Reports:
- [Hybrid Car Emissions Compared to Conventional Gasoline Vehicles](https://www.greencarreports.com/news/1104326_hybrid-car-emissions-compared-to-conventional-gasoline-vehicles)
8. Automaker websites:
- Most car manufacturers provide detailed information on the fuel efficiency and emissions of their hybrid car models.
