Qualitative research is based on a study from the documentary research, including the legal provisions of Revenue Code and other laws about imposing tax that was used in the Excise Tariff Act, B.E. 2527(1984), Customs Act B.E. 2469(1926), Petroleum Income Tax Act B.E. 2514(1971), Administrative Procedure Act, Academic articles, International Law in the relevant, the decisions of the Supreme Court and regulations and practices of an agency in the Revenue Department.