Briquettes of specified geometry and composition are produced to serve as feed material or "burden" in a moving-burden gasifier for the production of a synthesis or fuel gas from organic solid waste materials and coal, including especially, the so-called "caking" coals, as in the process of copending application number 675,918. The briquettes are formed from a well-blended mixture of shredded organic solid wastes, including especially, municipal solid waste (MSW) or biomass, and crushed caking coal, including coal fines. A binder material may or may not be required, depending on the coal/MSW ratio and the compaction pressure employed. The briquettes may be extruded, stamped, or pressed, employing compaction pressures in excess of 1000 psi, and preferably in the range of 2000 to 10,000 psi. The briquettes may be circular, polygonal, or irregular in cross-section; they may be solid, or concentrically perforated to form a hollow cylinder or polygon; they may be formed into saddles, pillows or doughnuts. The ratio of caking coal to shredded municipal solid waste is controlled so that each part of the predominately cellulosic organic solid waste will be blended with 0.5 to 3.0 parts of crushed coal. Suitable binder materials include dewatered sewage slude (DSS), "black liquor" rich in lignin derivatives, black strap molasses, waste oil, and starch. The binder concentration is preferably in the range of 2 to 6 percent. If coals high in sulfur content are to be processed, at least a stoichiometric equivalent of dolomite may be included in the briquette formulation to eliminate a major fraction of the sulfur with the slag.