Besley and Rosen (1998) were the first authors to empirically estimate the presence of vertical tax externalities. They tested it on gasoline and tobacco unitary taxes. However, they did not take into account the difference in cost of living across states: high cost areas pay less in real terms than low cost areas, since the nominal unit tax on cigarettes and gasoline does not differ according to the state in which it is applied. Consequently, we propose that vertical tax competition can be estimated by deflating all financial variables using the House Price Index (HPI), which is disaggregated by states.