Pre-ground plastics of small particle size not more than 2 mm are co-fed into a solid fossil fuel fed entrained flow partial oxidation gasifier. High solids concentrations in the feedstock stream can be obtained without significant impact on the feedstock stream stability and pumpability. A consistent quality of syngas can be continuously produced, including generation of carbon dioxide and a carbon monoxide/hydrogen ratio while stably operating the gasifier and avoiding the high tar generation of fluidized bed or fixed bed waste gasifiers and without impacting the operations of the gasifier. The subsequent syngas produced from this material can be used to produce a wide range of chemicals.