Areal and vertical distributions of petroleum viscosities within heavy oil reservoirs are important in designing well completions, optimizing field development and planning thermal and other recovery operations. Viscosities of oils in closely-spaced reservoir zones in heavy oil fields can vary substantially. Unfortunately, oil samples are often unavailable or too small for conventional laboratory viscosity measurements. In such cases, correlations between heavy oil viscosity and geochemical, chemical and physical parameters can be valuable for estimating working viscosities. Various geochemical-viscosity correlations were evaluated using a suite of heavy crude oils (API gravities < 150) from fields in the San Joaquin Valley, California. Whole, dewatered, crude oils where studied. Kinematic viscosities were measured at multiple temperatures. Elemental, organic acid, pour point and gravity analyses were completed, followed by compound class separations and gas chromatographic analyses. Statistical methods were used to assess correlations of various parameters with viscosity. Results were compared with correlations reported in the literature and evaluated in terms of linkage to models of field-wide degradation processes believed to account for formation of the heavy oils, with the goal of assessing these predictive models for viscosity variations with applications to viscosity mapping.