A customs duty anomaly that has periodically attracted interest is the 5 per cent tariff on imported four- wheel-drive vehicles (4WDs) compared to a 15 per cent tariff on imported passenger motor vehicles (PMVs). The tariff rate differential exists because there is no tariff classification that deals specifically with 4WDs. This Research Note examines the rationale for the lower tariff rate on 4WDs and its impact on passenger car sales.