The monoenic fatty acid methyl ester hydrogenation and isomerization over a supported nickel catalyst was studied at 0.02 less than or equal to P-H2 less than or equal to 0.50 MPa and 333 less than or equal to T less than or equal to 443 K. Batch hydrogenations at constant and variable hydrogen pressure were carried out to investigate the rate-determining steps. On the basis of the Horiuti-Polanyi mechanism, involving a half-hydrogenated surface intermediate, kinetic rate equations were systematically derived following the Langmuir-Hinshelwood-Hougen-Watson approach. Each set of rate equations was tested by means of a chi(2) method on its ability to describe the experimental curves simultaneously. The chi(2) was minimized by a stepwise optimization of model parameters. Furthermore, we used Bartlett’s test to reduce the set of most-likely rate expressions. The statistically most significant model assumes the formation of the half-hydrogenated surface intermediate as the rate-determining step and an equilibrium associative hydrogen adsorption. The rate equations are R-0 = m(c){[-(k(fo)(o,h) + )C-0 + <(k)over bar (iso) C-E]/[C-0> + C-E + (K-S/K-M)C-S]}KHPH[mol/(m(3) s)] and R-E = m(c){[-k(f,E)(E,h) + <(k)over bar (iso)>KisoC0]/[C-0 + C-E + (K-S/K-M)C-S]}KHPH[mol/(m(3) s)] with k(f,0)(0,h), k(f,E)(E,h) and <(k)over bar (iso)> (units : [kg(r)(kg(Ni) s MPa)]) the formation rate constants of the half-hydrogenated intermediate in the hydrogenation of cis-monoene and trans-monoene and in the isomerization path, respectively. K-iso is the equilibrium constant for the isomerization, K-S/K-M is the ratio of adsorption constants of saturated and monoene components, m(c) is the catalyst load [kg(Ni)/m(r)(3)], C-0, C-E, and C-S are the concentrations of methyl oleate (cis), methyl elaidate (trans), and methyl stearate, respectively [mol/m(3)], K-H is the adsorption constant of hydrogen [MPa-1], and P-H2 [MPa] is the hydrogen pressure. The activation energies of k(f,0)(0,h)K(H), h(f,E)(E,h)K(H), and <(k)over bar K-iso(H)> are 32.2, 28.1, and 47.2 kJ/mol, respectively.