Structures and energetics of reactants and transition structures of cycloadditions of allene (A), monofluoroallene (MFA), and 1,1-difluoroallene (DFA) with diazomethane, formonitrile oxide, cyclopentadiene, and furane have been investigated with the use of ab initio molecular orbital calculations. Structure optimizations were performed with both RHF/3-21G and RHF/6-31G* calculations but were limited to RHF/3-21G for the reactions of cyclopentadiene and furane. For these reactions as well as for the reactions involving DFA electronic energies were computed to the MP3/6-31G* level, whereas the full MP4/6-31G* level was also explored for all the other reactions. Kinetic contributions to activation enthalpies and entropies and solvent effects were also considered. Electronic activation energies are found to be very sensitive to the treatment of electron correlation and fail to converge to values unaffected by further theoretical improvements; indeed, the inclusion of full fourth order correlation (MP4) decreases the activation energies by 5-8 kcal/mol with respect to the preceding level of correlation (MP3). In contrast, the reactivity sequences of A, MFA, and DFA as well as regio and diastereoselectivities attain, in general, stable predictions even at rather low levels of calculation and agree well with experimental trends.