With the advent of more reactive catalysts, equilibrium RCM is observed quite often which may lead to a greater product distribution. The mechanism can be expanded to include the various competing equilibrium reactions as well as indicate where various side-products are formed along the reaction pathway, such as oligomers.
Although the reaction is still under thermodynamic control, an initial kinetic product, which may be dimerization or oligomerization of the starting material, is formed at the onset of the reaction as a result of higher catalyst reactivity. Increased catalyst activity also allows for the olefin products to reenter the catalytic cycle via non-terminal alkene addition onto the catalyst. Due to additional reactivity in strained olefins, an equilibrium distribution of products is observed; however, this equilibrium can be perturbed through a variety of techniques to overturn the product ratios in favor of the desired RCM product.
Since the probability for reactive groups on the same molecule to encounter each other is inversely proportional to the ring size, the necessary intramolecular cycloaddition becomes increasingly difficult as ring size increases. This relationship means that the RCM of large rings is often performed under high dilution (0.05 - 100 mM) (A)  to reduce intermolecular reactions; while the RCM of common rings can be performed at greater concentrations, even neat in rare cases. The equilibrium reaction can be driven to the desired thermodynamic products by increasing temperature (B), to decrease viscosity of the reaction mixture and therefore increase thermal motion, as well as increasing or decreasing reaction time (C).
Catalyst choice (D) has also been shown to be critical in controlling product formation. A few of the catalysts commonly used in ring-closing metathesis are shown below.