Liquid viscosity is an important fluid property that can affect the productivity of an oil and gas well. Therefore, petroleum engineers must investigate this parameter to determine the most efficient way to mitigate the impact, while improving the performance of an oil and gas well to save resources and overall cost for future projects. To investigate the research question on “How liquid viscosity affects well performance”, we elected to use PIPESIM to perform a sensitivity analysis on how API gravity affects oil production rate and well flowing pressure, since there is a strong correlation between API gravity and viscosity of a fluid. Beggs and Robinsons correlation forms the foundation of the method chosen. For a vertical well with a static pressure of 4000psi, a temperature of 175°F, API gravity of 32°API and a productivity index of 2.5STB/d/psi were some of the parameters adopted during this investigation. From the simulation, it was observed that the higher the API value, the higher the flowrate. Whereas the opposite effect was observed for the well flowing pressure as this significantly reduced, confirming an indirect relationship between the API gravity and viscosity. In addition, it was observed that the maximum operating conditions occurred between 40° and 46° API, as two values produced the same flowrate of 3163.95 STB/day offering the suggestion that after a certain degree of API gravity (viscosity) there would be no pronounced effect on further flowrate. To conclude, the findings will imply that viscosity has a negative impact on productivity, however, can be mitigated with methods such as gas injection, steam flooding and insitu combustion, in order to increase the API gravity.