In 1991, a tax differentiation was introduced to reduce air pollution from lead, particularly in the capital city, Bangkok. The tax was one element in a package of measures to increase awareness of the damage caused by leaded petrol, liberalise fuel markets and support oil companies to produce unleaded fuels. Consumers responded rapidly to the new price differential between unleaded petrol (THB (Thai baht) 14/litre) and leaded petrol (THB 15/litre) and within 30 days, the share of unleaded fuel had already risen to 30 per cent (Institute for Global Environmental Strategies, 2004).