Heavy oil is particularly known for the difficulty it presents in obtaining accurate fluid property measurements. The uncertainty of heavy oil fluid property measurements affects the quality of fluid property data which in turn affecting the accuracy of production forecast. In our investigation, we included the impact from certain heavy oil fluid property uncertainties, including live oil viscosity and saturation pressure [or the initial gas-oil ratio (GDR)]. The reservoir simulations were performed for case studies with a 9 degrees API reservoir fluid and geology similar to those typically found in the Faja region in Venezuela. Two basecases and the underlying process mechanisms were established, one assuming primary production process and one assuming steam-assisted gravity drainage process (SAGD). We then performed sensitivity studies of the different fluid property variations to determine the effect on the process performances. We found that the process mechanism dictated the magnitude of the sensitivity to different fluid properties. The uncertainties of the recovery prediction obtained from a reservoir simulator confirmed importance of selecting accurate fluid property data on the dynamic simulation prediction.