This paper outlines some of the environmental and economic implications of an additional CO2 tax of EUR 15/tCO2 in Slovenia in the period 2012-2030 in order to determine whether it yield a double dividend. Authors analyze (using E3ME model) different forms of revenue recycling by reducing the social security contributions of either the employers or the employees or by reducing the public deficit, in order to identify the optimal fiscal instrument for improving the environmental and economic welfare (double dividend). In this policy orientated paper authors argue that a reduction of employee social security contributions has more favourable effect than a reduction in employers' social security contributions.