Glossary
- Plug-in hybrid (PHEV)
- A car with a petrol or diesel engine plus a battery that can be charged from the grid and drive the car on electricity alone for a limited range.
- Full hybrid
- A car with an engine and a small battery charged by the car itself. It cannot be plugged in.
- Mild hybrid
- A car with a small electric motor that assists the engine but cannot drive on electricity alone.
- WLTP
- The lab test used in Europe since 2018 to set official fuel and CO2 figures.
- Utility factor
- The assumed share of driving a plug-in hybrid does on electricity, used to weight its official fuel figure.
- OBFCM
- On-board fuel and energy consumption monitoring: the meter that records a car's lifetime fuel use and distance.
- Charge-depleting mode
- Driving while the battery supplies energy. The engine may be off, or running to help.
- Charge-sustaining mode
- Driving with the battery at its minimum, so the car works like a regular hybrid.
- Benefit-in-kind (BiK)
- UK tax on company cars used privately, based on the car's official CO2 and, for low-emission cars, its electric range.
- Euro 6e-bis
- The emissions standard that introduced a stricter utility factor for plug-in hybrids from 2025.
- Gap
- On PluginRisk: real-world fuel use divided by the official figure.