We have calculated the standard enthalpies of formation Delta(f)H(298) of benzene, 8 benzene isomers, and 15 of their mono-, di-, and trihydrogenation products by the G2(MP2) and G2(MP2,SVP) ab initio methods. The ab initio results are used in conjunction with isodesmic "bond separation" reactions to obtain enthalpies of isomerization and hydrogenation, Delta(isom)H(298) and Delta(hyd)H,(298) which follow directly from the calculated total enthalpies at 298 K. G2(MP2,SVP) calculations are not, insofar as can be determined from the scattered experimental data, inferior to G2(MP2) calculations within the usual target uncertainty range of +/-2 kcal mol(-1).