Operating variables affecting the efficiency of the basic oxygen furnace (bof) and the level of contaminating elements in the steel product were investigated by the Bureau of Mines. Steel was made in a 400-pound-capacity bof designed to rotate on its vertical axis to increase the area of hot metal surface subject to oxygen attack. Hot metal for the bof was made by melting pig iron and scrap in an 18-inch-id cupola. The variables were bof speed of rotation, rate of oxygen flow, number of jets and angle at which they were machined into the oxygen-lance tip, temperature of hot metal, reactivity of lime, and temperature of scrap for the bof charge. Experiments were arranged according to a two-level fractional-factorial design. The effects of the seven variables were evaluated for 13 responses. The greatest ingot yield occurred while using the larger angle lance tip and jets. The most carbon burned per unit volume of oxygen resulted from rotating the bof and using the smaller angle lance tip. The largest sulfur transfer to the slag occurred at the higher hot metal temperature levels and higher rate of oxygen flow.