The economical recycling of waste materials to produce liquid fuel feedstocks is being investigated. Particular emphasis at the Pittsburgh Energy Technology Center (PETC) has been given to coal/waste coprocessing. Coal/waste coprocessing represents the conversion, into fuels and higher value products, of coal with a combination of any or all of the following : plastics, rubber, heavy oil, waste oil and paper. This study focuses on the rheology of various mixtures of coal, plastics, rubber and oil in order to facilitate their pumping in coal/waste coprocessing continuous units. The rheological properties of these mixtures determine their pumpability and the feed system requirements for the slurries. The viscosities of coal/waste mixtures were measured at various temperatures and shear rates. It was noted that these mixtures had non-Newtonian flow properties, hence their viscosities were a strong function of shear rate. The relative amounts of coal, plastics (and plastics type), rubber and oil were varied in order to evaluate their effect on apparent viscosity. A bench-scale continuous unit was used to evaluate the pumpability of slurries that represent mixtures that may be used in coal/waste coprocessing.