Disclosed is a continuous or discontinuous process for coking high-boiling aromatic hydrocarbons to form high grade carbon products having only a narrow range of variation of physical and chemical properties. High-boiling aromatic hydrocarbon mixtures are coked in thin layers according to a defined temperature/time program, and the functional relationship between layer thickness and optimum coking time, which applies to that program for the particular hydrocarbon mixture used, is determined by means of a simple preliminary experiment. A small quantity of the hydrocarbon mixture used is coked on a microscope hot stage under standardized conditions to determine the minimum coking temperature, the time to the final coking temperature and the dependence of coking time on the layer thickness.