A controlled-atmosphere cone calorimeter was used to investigate the burning of one epoxy/fiberglass and two brominated epoxy/fiberglass composites. The composites were tested in normal oxygen and oxygen-enriched environments (oxygen concentration up to 30 percent) at 25, 35, and 50 kw/m2 heat fluxes. Results indicate that the heat flux had a major effect on the ignitability of epoxy/fiberglass and brominated epoxy/fiberglass while the oxygen concentration had a minor effect. The ignitability of epoxy/fiberglass was similar to that of brominated epoxy/fiberglass except the critical heat flux for ignition. For epoxy/fiberglass, the peak mass loss rate, peak heat release rate, and total heat released increased with the increase of oxygen concentration and heat flux, and the average specific extinction area decreased with the increase of oxygen concentration and heat flux. For brominated epoxy/fiberglass, the peak heat release rate and total heat released increased with the increase of oxygen concentration. In comparison with epoxy/fiberglass, brominated epoxy/fiberglass self-extinguishes faster, and produces more carbon monoxide (CO) and less carbon dioxide (CO2) during burning. The upward flame spread rate and upward flame spread length of each composite obtained in separate experiments can be correlated with the peak heat release rate data obtained from the cone calorimeter tests. The controlled-atmosphere cone calorimeter was effective in differentiating the burning of epoxy/fiberglass and brominated epoxy/fiberglass and is an effective tool for selecting materials to be used in the oxygen-enriched environments.