Ozone (O-3) and ozone/hydrogen peroxide (O-3/H2O2) can be used in water treatment facilities to remove many organic micropollutants with taste, odor, and color implications. The effects of O-3 and O-3/H2O2 on the formation of disinfection byproducts (DBPs) in subsequent chlorination and chloramination processes, however, are not well determined. In this study, we compared the yields of a series of regulated and emerging DBPs during sequenced O-3-Cl-2, O-3/H2O2-Cl-2, O-3-NH2Cl, and O-3/H2O2-NH2Cl oxidation of 11 samples, each with different hydrophobicity, bromide concentration, soluble microbial products, and humic substances. For most water, pretreatment with O-3 and O-3/H2O2 increased the formation of chloral hydrate (CH), trichloronitromethane (TCNM) and haloketones (HKs) but lowered the yields of haloacetonitriles (HANs) during chlorination processes. Compared with O-3 alone, O-3/H2O2 in combination generated more CH and HKs during chlorination, and their extents of formation appeared to depend on the O-3 doses. In terms of chloramination, both O-3 and O-3/H2O2 reduced THM, HAA, and HAN formation significantly without increasing CH, TCNM, or HKs. These results suggest that O-3 or O-3/H2O2 pretreatments may provide some benefits for the chloramination process in controlling regulated and emerging DBPs in waters without high bromide content. (C) 2012 Elsevier B.V. All rights reserved.