Complex solid hydrofulleride mixtures were synthesized by prolonged hydrogenation of C-60 at 120 bar hydrogen pressure, 673 K temperature, and different reaction periods. The high degree of hydrogenation was confirmed by infrared spectroscopy and X-ray diffraction. The identity of hydrogenation products was determined by high-resolution field desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry. Despite partial gas-phase fragmentation of hydrofullerene ions during mass analysis, the data suggest that the synthesized mixtures consist of mostly C58-60Hx hydrofullerenes. Increasing the duration of hydrogenation results in synthesis of C59Hx and C58Hx as major products. Possible hydrofullerene fragmentation pathways during both material synthesis and mass spectrometric analysis are discussed. Gas-phase fragmentation in the mass spectrometer arises from hydrofullerene ions C60Hx+ with x > 40 and C59H44+ with drastically decreased molecular stability relative to the known C60H36.