This research investigated the influence of bromide-ion concentrations upon trihalomethane (THM) formation and speciation. There is some speculation that bromide will increase the amount of THMs on a mass and/or molar basis. Previous research had indicated that bromide will affect the speciation to form the more brominated forms of THMs, but the extent of this speciation has not been clearly defined. Speciation is important when evaluating THM removal processes. The brominated species may require activated carbon for removal as opposed to air stripping for removal of the volatile species (chloroform). To investigate the role of bromide ion, a half-fractional, factorial matrix was used in which the DOC, pH, and temperature were varied at two levels; chlorine dosage and bromide-ion concentration were varied at three levels; and time was varied at five levels (up to six days). Over 750 experimental observations were used to generate five empirical models employing the six factors. An empirical model was generated to determine the mass for the THM species and to estimate the Total THMs. The results indicate the following: 1) all variables were positively correlated to trihalomethane formation; 2) bromide-ion concentration is a significant factor for each species; 3) bromide increased the THM yield both on a mass and a molar basis; and 4) bromide shifted the species distribution almost completely suppressing chloroform production in favor of the brominated THM species.