CROSS-BORDER SHOPPING AND THE OPTIMUM COMMODITY TAX IN A COMPETITIVE AND A MONOPOLY MARKET

Using a partial equilibrium model, optimality rules for a commodity tax are derived for an economy that is exposed to cross-border shopping. In a competitive market, the conventional inverse elasticity rule is shown to be valid with the qualification that it is the elasticity of domestic rather than total demand that matters. With a foreign monopoly, the inverse elasticity is modified by a tax-shifting effect. When the supplier is a multinational firm, price repercussions abroad should be taken into account. The implications for domestic taxation of the prices and taxes set abroad are also examined.