This paper presents a micro-econometric approach to corporate tax modelling. Using firm level panel data of UK companies in three diverse sectors, the paper examines the impact of different variables on corporate tax liabilities of the firms. Many strong results stand out which suggest that firms reduce their tax liabilities through different channels and tax sheltering activities to maximise �after-tax� profits. The evidence shows, inter alia, that not only are trading profits and capital gains important determinants of corporation tax payments but so also are their components, such as gross profit, cost of sales, expenses, and even one-off �exceptional items� and �extraordinary items�. The results also indicate that firms� size, organisational structure, investments, and financial and dividend policies are important factors impacting on corporate tax liabilities. Moreover, different tax reliefs and allowances are strongly associated with corporation tax payments asymmetrically. The findings have implications for microsimulation modelling, financial transparency, and corporate governance.