The rheological properties of petroleum coke-water slurries (PWS) were examined and modified using polyvinyl alcohol (PVA), naphthalene sulfonate (NS), and xanthan gum (XG). PVA and NS were both very effective at reducing the slurry viscosity. Adsorption isotherms showed that PVA and NS must be adsorbed to the, particle surface to be effective; the viscosity cannot be reduced further once the particle surface is saturated. Decreasing the slurry viscosity also caused very poor stability against settling due to gravity. Adding XG to PVA-treated slurries gave strong shear-thinning behavior, which allowed for excellent stability. PVA and XG are practical and effective for producing PWS with ideal rheological behaviors. (C) 2016 Elsevier B.V. All rights reserved.