Gears used in gearboxes and those used in rear axles are subject to constantly increasing demands for reliability, performance and efficiency. To meet the requirements of the future market computer aided engineering, CAE, is becoming more and more vital in order to understand the onset and cause to failure and to optimize for best possible performance. The aim of this master thesis was to pave the way for numerical modelling as a complement to testing and to give insight in how the problem of simulating gears with oil and surface roughness incorporated can be addressed. Moreover, as part of this, the work was to be conducted in order to give insight in possibilities as well as shortcomings with present tools. Therefore a numerical tool which is capable of indicating the load carried by the asperities and the separating lubricant film during the event of a gear mesh has been developed. Several contact mechanics codes and different EHL formulas has been studied in order to provide alternative foundations to the gear simulation model. The model accounts for real surface topographies, different oil formulations as well as operational conditions and gear designs. Results show that the model visually correlates to test gears subjected to similar conditions in terms of critical areas on the gear flank. Even though validation is required to reveal model accuracy, at present, the model can be utilized to indicate how different conditions affect the asperity and lubricant load share and thus what combination that is most beneficial in terms of better performance and prolonged service life. In addition, a local scale asperity simulation where single asperities have been subjected to numerous collisions has also been developed. Results show that there is very promising potential in terms of future development as the model comprises the ability to potentially capture the initial state on the formation and development of a micropit.