A comparison of the oxygen recombination timescale with the cooling timescale at different densities. Low density favours the appearance of an overionised plasma, because the recombination timescale lowers proportional to the density, as does radiative cooling, but radiative cooling only becomes important at log T ≤ 10⁶   K. These curves where calculated using LMC abundances. It should be noted that a plasma at LMC abundances is less likely to reach an over-ionised state at T < 10⁶ K, because of the lower radiative cooling rate.