New analytical tools, products, and techniques have greatly improved fracturing treatments. Ongoing research will continue to optimize this stimulation method for enhancing hydrocarbon recovery. This concluding part of a series describes the additives and proppants available for designing effective treatments. Some additives discussed are these: antifoaming agents, biocides, buffers, clay stabilizers, crosslinkers, diverting agents, fluid-loss additives, friction reducers, gel breakers, production chemicals, surfactants, and temperature stabilizers. Some proppants discussed are these: sand, resin-coated sand, ceramic beads, and limited amounts of sintered bauxite.