This paper investigates the causal impacts of mining fiscal systems on generating resource rents from oil and gas extraction. This study covers 81 oil and gas producing countries during the period 1970-2015. It is found that a resource rent tax or its combination with a gross royalty tax perform better than a gross royalty tax in generating oil and gas rents. The significantly positive impacts of this mining fiscal system, however, only happen in developing countries, democratic countries, or countries with greater freedom. In developed nations, non-democratic countries, and countries with lower levels of freedom, the impacts disappear.