In this study, we examine the cross sections of 18,19,20O + 12C fusion reactions at energies near and below Coulomb barrier within the optical model. To propose alternative density distributions for theoretical studies of fusion reactions of oxygen isotopes (18,19,20O) and carbon target, we evaluate three different density distributions of 18,19,20O and 12C nuclei. Moreover, we apply two different theoretical approaches which consist of semi-microscopic and fully-microscopic in order to make a comparative study. The theoretical results are compared with each other as well as the experimental data. It is seen that the results are in good agreement with the data. The evaluated methods and density distributions are presented to be alternative ways in explaining the fusion cross sections of 18,19,20O + 12C systems. Finally, we show the effect of weak imaginary potential in fitting the experimental data.