One of the main challenges associated with the production of heavy or extra-heavy crude oil is transportation of the oil by pipelines, particularly without the prior reduction of the oil viscosity to acceptable values to ensure oil fluidity in the pipelines. The reduction of viscosity can be obtained by various sophisticated methods. In this study, we investigated different blending techniques to reduce the viscosity of heavy crude oil. The blending of Middle East heavy crude oil with light crude oil or with one of its distillates, such as kerosene or diesel, as diluents was conducted over the entire range of weight fractions at 20 degrees C and atmospheric pressure. The heavy oil viscosity was decreased from 4000 to 500 cP, representing an 88% reduction. The experimental data were fitted with an empirical equation, and the results were satisfactory, with an average absolute value of the deviation of 0.0015 cP. A negative performance of the heavy oil with diluent mixtures was identified based on the asphaltene precipitation phenomenon, which was found to depend on not only the type and composition of the diluents used but also the concentration of each diluent. To obtain additional insight into asphaltene precipitation, qualitative studies were performed with scanning electron microscopy imaging and dynamic light scattering. Compared to the other diluents, kerosene distillates performed well with a specific heavy crude oil sample under our testing conditions. The addition of 0.5-2 wt % of a solvent mixture of polar protic hexane-1-ol and nonpolar toluene to the crude oil and diluent mixture was found to successfully delay the precipitation of asphaltene in these low-viscosity mixtures.