  The class II masers of methanol are associated with the early stages of
formation of high-mass stars. Modelling of these dense, dusty environments has
demonstrated that pumping by infrared radiation can account for the observed
masers. Collisions with other molecules in the ambient gas also play a
significant role, but have not been well modelled in the past. Here we examine
the effects on the maser models of newly available collision rate coefficients
for methanol. The new collision data does not alter which transitions become
masers in the models, but does influence their brightness and the conditions
under which they switch on and off. At gas temperatures above 100 K the effects
are broadly consistent with a reduction in the overall collision cross-section.
This means, for example, that a slightly higher gas density than identified
previously can account for most of the observed masers in W3(OH). We have also
examined the effects of including more excited state energy levels in the
models, and find that these play a significant role only at dust temperatures
above 300 K. An updated list of class II methanol maser candidates is
presented.
