Heavy crude oil (density of 0.9571 g/cm(3) at 288 K and kinematic viscosity of 7160 mm(2)/s at 303 K) and natural gas condensate (density of 0.7848 g/cm(3) at 288 K and kinematic viscosity of 0.764 mm(2)/s at 303 K) were sampled from Omani oil fields. The oil was mixed with condensate (5-50 vol %), and the mixture viscosities were measured at the temperature range of 293-348 K. A drastic decrease in kinematic viscosity was achieved. An addition of about 12 vol % of condensate gave a viscosity of 265 mm(2)/s at 303 K. This made it easier to transport the heavy oil mixtures. The experimental data for the kinematic viscosity [v (mm(2)/s)] as a function of the gas-condensate fraction (phi) and temperature [T(K)] could be described by an equation: ln(ln(v)) ( k(1) + k(2)center dot T) + (k(3) + k(4)center dot T)center dot phi with a high accuracy. Blends of the heavy oil and the gas condensate were stored to evaluate their stability. Results showed less than 0.05 wt % sludge formation after 2 months.