In this study, the co-slurryability of hazardous solid waste-oily sludge and high-sulfur-petroleum coke (HSPC), in an oil refinery was evaluated. The effects of pre-treatment and method of adding oily sludge, on the co-slurryability of coke-oily-sludge slurry (COSS); maximum solids loading, rheological characteristics, and stability of slurry, were thoroughly investigated. The experimental results showed that with 5.0 wt% adding ratio of modified oily sludge (MOS), COSS with a maximum solids loading of 68.7 wt% was obtained, and mostly corresponded to coke-water slurry (CWS) with a maximum solids loading of 68.5 wt%. As the percentage of MOS increases, the yield stress and thixotropic loop area of COSS also gradually increases. COSS is a pseudoplastic fluid, and shows a different behavior as compared to CWS (with shear-thickening behavior). MOS played the role of a stabilizing agent, and therefore the storage time of COSS could be prolonged to more than 15 days. (C) 2013 Elsevier Ltd. All rights reserved.