The molar polarization (product of polarization level and concentration) has been proposed as a more useful hyperpolarization metric than the polarization level alone . The molar polarization achieved in the current experiment is estimated to be 6.12% × (49 ± 1) mM = 3.00 ± 0.06 mM (see Supporting Information). Figure compares the observed 13 C-polarization as a function of bubbling time τ B , for protocols (b) and (c). Since these protocols use the same singlet-to-magnetization conversion procedures, differences in performance may be attributed to the chemical and spin dynamics during the hydrogenation. The markers represent experimental data, whereas the solid curves represent numerical simulations. For protocol (b), which has no special intervention during the hydrogenation, the 13 C-polarization quickly reaches a plateau at a relatively low level. For the WOLF+STORM approach (protocol (c)) the build-up of 13 C- polarization continues to longer times with a plateau reached at τ B = 15 s. No significant reduction in 13 C-polarization was observed even beyond 20 seconds of bubbling. These data support the hypothesis that the simultaneous WOLF+STORM fields suppress singlet-triplet mixing during hydrogenation. The solid lines in figure show simulations derived by a Monte-Carlo procedure which combined many spin dynamical trajectories initiated at random times, according to a statistical model of the chemical kinetics. Details are given in the Supporting Information. An acceptable match between experiment and simulation is attained for both protocols (b) and (c), assuming an effective hydrogenation rate constant given by k eff = 0.05 ± 0.01 s -1 and a singlet order decay time constant T S of at least 60 seconds. This indicates that singlet spin order accumulates on the proton pair during the hydrogenation under WOLF+STORM irradiation.