Response to lead phase out in European countries depends on a number of factors including refinery configuration and vehicle population.Vehicle populations differ widely in different EU member states, and in some countries engineering changes made during the 1970s and 1980s have left the year 2000 vehicle populations able to operate on unleaded gasoline with no problems. For various demographic reasons, in certain other countries, a substantial proportion of the vehicle population still requires lead or an alternative additive to provide protection against the well known problem of valve seat recession. Benefits can arise from the use of additives able to increase both octane quality and to provide protection from valve seat recession. A development programme was undertaken to produce an additive formulation which could combine octane enhancement with excellent protection from valve seat recession. The programme involved vehicle and engine tests designed to quantify the performance of the additive and to assess its suitability for widespread use. These tests included valve seat recession performance, and octane determinations.