The magnetizability of a large number of hydrocarbons-saturated, unsaturated, and aromatic-have been investigated by ab initio methods at the Hartree-Fock level. Gauge-origin independence and size extensivity are imposed by the use of London atomic orbitals (also known as gauge-invariant atomic orbitals). Using a standard basis set adapted for magnetizabilities, results close to the Hartree-Fock limit are obtained. Correlation has a moderate effect on the magnetizabilities. Using an overall scaling factor for the Hartree-Fock results, we obtain magnetizabilities within the experimental error bars for most of the molecules considered. The calculations suggest that the observed gas-phase magnetizabilities contain a calibration error.