However, analysis from the past few years has shown that the real-world utility factor is significantly lower than the official values from vehicle type approvals (such as the World Harmonised Light Vehicle Test Procedure). The European Commission published a
report finding that the real-world CO2 emissions from PHEVs were on average 3.5 times higher than the laboratory values. A main factor behind this discrepancy is that PHEVs are not charged and driven in full electric mode as frequently as assumed. A separate
study has suggested that the real-world utility factor is lower for company cars compared to privately owned cars, because those vehicles tend to be charged less frequently. Increasing PHEV charging and the use of the battery mode would result in greater reductions in emissions, but such measures are difficult to enforce.