Tax Gap Assessment Between Oil-Tax and Non-Oil-Tax Revenue in Nigeria: Practical Measures for Trimming the Tax Gap in Non-Oil Tax

Oil is inarguably a non-renewable source of energy. Thus, some day somehow it would run out and run dry. Nigeria is found to be one of the countries of the world that over-rely on oil-tax revenue, against the non-oil tax revenue. However, to gain research evidence into this, the study embarked on the assessment of their tax gap, to determine which reported a wider or severer tax gap. Ex-post facto design was the research design deployed since quantitative data are already available, and obtained from Federal Inland Revenue Service, Nigeria. Regression statistics (applied with the aid of SPSS, ver. 25) was utilized for the data analyses and test of hypothesis. The study found that, although non-oil tax revenue recorded a stronger correlation (81.3%), it has a significantly wider tax gap – 40% above that, reported by oil-tax. From these finding and conclusion, the study recommended, among others, looking the way of non-oil tax revenue, such as investment in cleaner and more sustainable energy sources, agriculture, and services; the review of some of the non-tax rates to adapt them to the dynamic economic realities; and provision of greater enforcement resources to tax authorities for more effective tax administration.