Here's why:

* Conduction is the transfer of heat through direct contact between molecules. While conduction does occur in gases, it's less efficient than in solids or liquids because the molecules are farther apart.

* Convection is the transfer of heat through the movement of fluids (liquids or gases). Gases, being fluids, transfer heat primarily through convection. This movement can be caused by differences in temperature (natural convection) or by external forces like fans or wind (forced convection).

* Radiation is the transfer of heat through electromagnetic waves. Gases can both absorb and emit radiation, but this is a separate mechanism from convection.

Therefore, convection is the primary mode of heat transfer in gases.