The possibility of synergism in the Joule-Thomson effect for gaseous mixtures has been analyzed using the Van der Waals, Redich-Kwong, Soave and Peng-Robinson equations of state, in the low pressure range where the behaviour of the mixture can be described by the virial equation of state truncated after the second term. It is shown that synergism is possible and that in this low pressure range none of the equations is capable of predicting an extreme value for the differential isenthalpic Joule-Thomson effect.