The mechanism of epoxidation of the olefins cis- and trans-stilbene, styrene, and norbornene by the oxidant [Ru-IV(bpy)(2)(py)(O)](2+) has been investigated in acetonitrile solution by both conventional product analysis (GC-MS and H-1 NMR) and newly developed global kinetic analysis techniques. Under 1:1 stoichiometric reaction conditions (15 mM) the organic products from the oxidations of cis- or trans-stilbene included unreacted stilbene (>50%), stilbene oxide (<50%), benzophenone (similar to 6%) and trace amounts of diphenylacetaldehyde. In the case of trans-stilbene, use of the O-18-labeled oxidant showed that the oxygen atom of its Ru-IV=O2+ group was the predominant source of the oxygen in the epoxide products and a major contributor to the oxygen content of benzophenone. Under similar conditions, the oxidations of styrene and norbornene gave styrene oxide and exo-norbornene oxide as products by H-1 NMR. Kinetic studies were performed under pseudo-first-order conditions with a large excess of the olefins. Factor analysis of UV-vis spectra vs time for each reaction revealed the presence of five colored components and four distinct kinetic processes. In the case of trans-stilbene, the initial reaction was well-separated from the following steps, allowing a full global kinetic fit to be obtained to a multistep model. The initial stage involved net oxene insertion into the double bond of the olefin to form the Ru(II) epoxide complex, [Ru-II(bpy)(2)(py)(epoxide)](2+), without evidence for an intermediate. This was followed by a competition between its rapid oxidation by Ru-IV=O2+ and solvolysis by CH3CN. in the oxidation step both the Ru(III) epoxide and [Ru-III(bpy)(2)(py)(OH)](2+) are formed. Once formed, Ru-III-OH2+ was found to react further via initial disproportionation to Ru-IV=O2+ and Ru-II-OH22+.