The IEA carries out a comprehensive programme of energy co-operation among its member countries, each of which is obliged to hold oil stocks equivalent to 90 days of its net imports. Research shows that a mix of instruments is needed to address the rebound effect, but that instruments that ensure high prices must be part of the policy package (EC, 2011b, pp. The optimal tax rate may differ depending on the goal pursued by the tax (e.g. revenue raising, carbon pricing, promoting energy efficiency or slowing rebound effects). The objective of environmental taxation must be clear and may depend on the country context.