An experimental study was conducted to measure the effects of oxygen entrainment on the transport of CO in building fires, and to develop a procedure for estimating CO levels during a building fire. Experiments were performed with an insulated 1/4-scale room connected to the side of a 1/4-scale hallway forming a L-shape. Measurements of CO, unburned hydrocarbons (UHC), CO₂, and O₂ concentrations and temperature were performed within the compartment, the hallway and post-hallway in the exhaust duct. The level of CO transported to remote locations from the burning room was hypothesized to be most significantly affected by the oxygen entrainment into the compartment fire gases entering the hallway. With a fixed size opening connecting the compartment to the hallway, the oxygen entrainment was varied by changing the depth of the oxygen deficient hallway upper-layer. In experiments where compartment fire gases entered the hallway completely surrounded by oxygen deficient combustion gases, post-hallway CO yields were measured to be as much as 23% greater than CO yields measured inside the compartment, despite the presence of external burning. With deep upper-layers in the hallway, geometric effects were not observed to significantly affect the transported level of CO. Instead, the CO level was a function of the compartment stoichiometry and the occurrence of external burning. / Ph. D.