High voltage pulsed electrical discharges in water are of interest for a number of applications, for example, in chemistry, water treatment, electrical transmission, and bioengineering, because of the formation of highly reactive molecular and radical species (including the hydroxyl radical). While the existence of hydroxyl radicals in these systems has been demonstrated by emission spectroscopy, accurate quantification of the rates of formation of this species is needed to develop insight into the means by which electrical discharge can promote useful chemical reactions. This paper focuses on quantification of hydroxyl radicals using chemical probes (dimethyl sulfoxide (DMSO) and disodium salt of terephthalic acid (NaTA)).