1) "Viscosity in gases arises principally from the molecular diffusion that transports momentum between layers of flow. The kinetic theory of gases allows accurate prediction of the behavior of gaseous viscosity. Within the regime where the theory is applicable: Viscosity is independent of pressure and Viscosity increases as temperature increases." "In liquids, the additional forces between molecules become important. This leads to an additional contribution to the shear stress though the exact mechanics of this are still controversial. Thus, in liquids: - Viscosity is independent of pressure (except at very high pressure); and - Viscosity tends to fall as temperature increases (for example, water viscosity goes from 1.79 cP to 0.28 cP in the temperature range from 0 °C to 100 °C); see temperature dependence of liquid viscosity for more details. The dynamic viscosities of liquids are typically several orders of magnitude higher than dynamic viscosities of gases." Source and further information: http://en.wikipedia.org/wiki/Viscosity 2) "As a gas gets higher in temperature it has more collisions, and thus, more friction with its neighboring molecules." Source and further information: http://wiki.xtronics.com/index.php/Viscosity