Distillation column base levels are known to exhibit inverse action in certain cases, and this is detrimental to column control performance when reboiler duty is set by the base level controls. This inverse response behavior in level is known to arise due to two factors, namely the reboiler swell and the froth density effects. Inverse action due to reboiler swell effects depends upon the operating pressures and also on the reboiler type. Inverse action due to the froth density effects is dependent on the operating regime and tray design. It was found that, in general, for high-pressure columns, inverse action is unlikely due to either the froth density or the reboiler swell effects. For low-pressure columns, inverse action can be significant. Contrary to the reported literature, it was concluded that froth density effects are not as likely to be a significant cause of inverse action in reboiler levels as reboiler swell.