Reviewed 2026-10-05 · 2 min read · 3 original sources
A plug-in hybrid can drive without tailpipe emissions while its engine is off, but it can also burn fuel. European rules sometimes group qualifying PHEVs with zero- and low-emission vehicles, a category that does not mean every vehicle in it is zero-emission in everyday use. [1][2][3]
The studies compare first-registration cohorts, not stated model years or manufacture years. The 2021-versus-2023 PHEV cohort comparison is explicit, but does not identify battery chemistry or establish behavior for every PHEV.
We separate vehicles from before 2023 and 2023 onward. A report’s publication date does not establish a vehicle’s model year or a battery’s manufacturing date.
No separate result for this group is established by the cited evidence.
“Not reported” means the source does not disclose it. Model year, first registration, vehicle assembly and battery manufacture are different dates. Unmatched studies cannot establish how much newer batteries improved.
European Commission and ICCT monitoring data describe fleet-average PHEV cohorts without makes or models. The regulatory label covers a defined vehicle category, not named brands; findings are cohort- and policy-level, so no manufacturer comparison is available.
All manufacturers are OEMs. These groups describe brand focus, not a quality ranking or country of origin. EV-focused brands can also sell plug-in hybrids. Results apply to the identified models, batteries and conditions.
Includes historical inputs from before 2023. Vehicle cohorts, observation periods and publication dates are listed separately.
A battery-electric car has no combustion engine and produces no tailpipe emissions while driving. A plug-in hybrid electric vehicle (PHEV) combines a rechargeable battery and electric motor with a combustion engine. Depending on charge, speed, temperature, route, and vehicle control, it may run on electricity alone, burn fuel, or use both. So “zero tailpipe emissions” can accurately describe a PHEV during electric-only operation; it does not describe every trip or the car’s capability as a whole. Calling the category simply zero-emission hides that distinction. [1][2]
Part of the confusion comes from European policy language. Regulation (EU) 2023/851 defines a zero-and-low-emission incentive category covering cars with type-approved tailpipe CO2 from zero up to 50 grams per kilometre. It explicitly includes well-performing plug-in hybrids alongside battery-electric and fuel-cell cars. That is a combined “zero-and-low” category with a test-cycle threshold, not a finding that each qualifying PHEV is emission-free on the road. [1]
The European Commission’s first report used on-board fuel-consumption monitors in cars registered in 2021. From a dataset of about 600,000 cars, it found average PHEV real-world CO2 emissions 3.5 times their laboratory type-approval values. The Commission said charging and electric driving occurred less often than the test assumptions implied. [2]
ICCT’s September 2026 working paper expanded the evidence to about 920,000 PHEVs registered across Europe from 2021 through 2023. Its average real-world emissions were 130 gCO2/km against 37 official g/km for the 2021 cohort, and 134 against 29 for the 2023 cohort. Meanwhile, the share of driving in electric mode fell as electric ranges grew. The official utility-factor formula assumed longer range would mean proportionately more electric driving; the on-board data show that assumption did not hold for these cohorts. [3]
These averages do not mean every PHEV is driven with an empty battery or that a charged PHEV has no useful electric operation. They do show why a low official test value cannot stand in for zero emissions across real-world use. The precise description is that PHEVs can drive electrically for some or much of their travel, while retaining an engine that emits when it runs. For an emissions comparison, name the mode, pollutant, driving conditions, and measurement: an electric-only trip can have zero tailpipe emissions; a PHEV fleet or vehicle over mixed operation cannot be assumed to have them. [2][3]
Data period: EU PHEV first-registration cohorts from 2021–2023; official Commission analysis of 2021 registrations; research published 2023–2026
Same ICCT analysis, unit, powertrain category, geography and first-registration cohorts. The paired values compare average type-approval CO2 with OBFCM-derived real-world fleet-average CO2 for the approximately 920,000 PHEVs registered in Europe from 2021 to 2023. They are cohort means, not a claim that every individual car emitted these amounts.
A PHEV can be zero-emission while operating in electric-only mode. Its combustion engine means the vehicle is not zero-emission across all use, and European zero-and-low-emission policy categories should not be shortened to “zero-emission.” [1][2][3]
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