The rheological properties of four slurry fuels were studied and a variety of complex flow phenomena was observed. The slurry fuels contained ca. 50% by weight carbon black particles with an average particles size of 0.1 μm. In order to characterize the viscoelastic and plastic properties of the slurry fuels, stress growth and steady‐state experiments were performed over a wide range of shear rates. The slurry fuels were shear thinning under most conditions and were shear thickening at extreme conditions. They exhibited thixotropic behavior, with the degree of thixotropy depending on the specific slurry. Most of slurries had a yield stress ranging from 2 to 110 dyn / cm 2 . For the slurries which had a large yield stress, stress overshoot was observed. The stress overshoot increased with increasing shear rate. The maximum stress overshoot occurred at lower shear strains, the higher the shear rate. Temperature effects on the shear viscosity and yield stress were also studied. An unusual temperature dependency was found for one slurry and can be explained as a result of structural formation. A preliminary analysis was developed by using a modification of our kinetic‐elastic theory to describe the pseudoplastic and thixotropic behaviors of materials that exhibit a yield stress. The temperature effect on viscosity was also analyzed in terms of this model.