The transport and discharge of ballast water has been recognized as a major vector for the introduction of invasive species. Chemical oxidants, long used in drinking water and wastewater treatment, are one treatment method for the control of invasive species currently being tested for use on ships. One concern when a ballasted vessel arrives in port is the adverse effects of residual oxidant in the treated water. The most common oxidants include chlorine (HOCl/OCl-), bromine (HOBr/OBr-), ozone (O3), hydrogen peroxide (H2O2), chlorine dioxide (ClO2), and monochloramine (NH2Cl). The present study was undertaken to evaluate the sunlight mediated photochemical decomposition of these oxidants. Sunlight photodecomposition was measured at various pHs using either distilled water or oligotrophic Gulf Stream water for specific oxidants. For selected oxidants, quantum yields at specific wavelengths were obtained.