An improved coking process for normally solid carbonaceous materials wherein the yield of liquid product from the coker is increased by adding ammonia or an ammonia precursor to the coker. The invention is particularly useful in a process wherein coal liquefaction bottoms are coked to produce both a liquid and a gaseous product. Broadly, ammonia or an ammonia precursor is added to the coker ranging from about 1 to about 60 weight percent based on normally solid carbonaceous material and is preferably added in an amount from about 2 to about 15 weight percent.