The effect of altering compositions of cementless pressed building units on compressive strength was examined through tests of specimens composed of oil shale and coal fly ash binder, sand and water. The influence of compaction pressures applied in the molding process and various curing conditions on compressive strength were studied. Through X-ray diffraction analysis, crystalline phases in cementing matter that was generated in moist and steam curing were identified. Results of production experiments in a block-making plant are described. It is shown that high-performance blocks, corresponding to standard requirements, can be manufactured on current production equipment.