The paper examines the sensitivity of Nigeria's taxable capacity towards the tax efforts undertaken between 1980-2010. Utilizing the Ordinary Least Squares (OLS) regression statistic, the paper sought to ascertain the level of response of those variable indicators which were representative of the nation's taxable capacity, to government's tax efforts. The weak estimates of most of the major tax sources attests to their poor response to the tax measures undertaken are the stated period insensitivity to government tax efforts culminated in excess taxable capacity which was explorted over the stated period. The study reveals, that most of the variable indicators were largely unresponsive to the tax efforts undertaken, resulting in excess taxable capacity that was unexploited. The tax measures undertaken thus failed to achieve optimum aggregate tax yield. Government needs to intensify its tax efforts in order to exploit the excess taxable capacity.