The increasing demand for public goods and services due to economic growth has exposed the Indonesian budget to the problem of fiscal sustainability. To deal with the problem, an effective tax revenue collection system is the only viable option given the current budget situation where increasing government expenditure demands for fiscal independence. To be able to increase tax revenue, an analysis of real tax potential is critical. This study addresses the issue of the gap between the potential tax revenue and actual collection. We place emphasis on three taxes, namely Personal Income Tax, Corporate Income Tax and Value Added Tax, as they have been major contributors to Indonesian tax revenue. A large gap is found, leaving a wide room for improvement by narrowing it down through tax reforms. By assessing tax variables (i.e. tax rates, tax base and collection system), the study further discovers that instituting reforms to improve the collection system is more desirable than adjusting the rates or bases. Moreo