Profitable companies are expected to pay a 30% companies income tax on their profits earned in Nigeria. However, many companies in Nigeria pay far less due to their application of tax avoidance strategies. This paper report how profitable companies in Nigeria are able to successfully employed the loopholes in the Nigerian tax system to significantly lower their effective tax rate over the past five years. The paper examines 68 companies that are consistently profitable in each of the five years between 2014 and 2018, excluding companies that experienced even one unprofitable year during this period. From the analysis, this paper finds that as a group, the 68 companies examined paid an effective companies income tax rate of only 16.45% over the five-year period -far less than the statutory 30% companies' income tax rate. Based on the evidence, this paper advocate for a strong alternative minimum tax that can do the job it was originally designed to do thereby bring about transparency, equity and fairness in tax payment in Nigeria. This paper adds new knowledge to the understanding of the state of tax avoidance in Nigeria. Finally, identifying firms' aggressive tax planning strategies will close the tax loopholes and boosting tax revenue in Nigeria.