The Auto-Oil process is a central ingredient of the EU’s battle to control vehicle pollution. Previous research has focused on the policy-making phase, particularly the imbalanced stakeholder involvement. The time is therefore ripe to explore the impact of the Auto-Oil Directives on the industrial target groups, i.e. policy effectiveness. More behavioural change has taken place in the oil industry than in the car industry, and especially in the North. It is likely that EU’s institutional machinery and its various mechanisms did help bring about these behavioural changes, by bringing about the new knowledge that cleaner fuel was essential in order to attain the agreed goals between the EU and the car industry on reduced CO2 emissions. More importantly, the EU initiative to adopt a more stringent sulphur-in-fuels policy increased the pressure on the oil industry especially. But factors other than the EU’s institutional machinery need to be taken into account in order to explain the events of recent years. For instance, EU policy development and domestic initiatives in this field clearly affected each other. Hence, in order to clarify Auto-Oil effectiveness further, both vertical and horizontal interactions need to be better understood.