As a result of the large number of decay pathways presented to a fissioning nucleus, there is a large variation in the final products. Fragment masses are normally distributed about two peaks centred at A ≈ 95 and A ≈ 140. Spontaneous fission does not favour equal-mass fragments, and no convincing explanation has been found to explain this. In rare instances (0.3%), three or more fission fragments may be created. Ternary products are usually alpha-particles, though can be as massive as oxygen nuclei.