The Globe and Mail reports in its Tuesday edition that a growing number of carriers have adopted flexible pricing for luggage based on factors such as demand, flight routes and time of purchase. The Globe's Erica Alini writes that flexible rates for bags and other add-on services are likely to drive up the overall cost of flying at peak travel times. The changes also make it harder for consumers to gauge how much their total flight cost might be before committing to a booking. Among the Canadian carriers surveyed by The Globe, only Porter Airlines said it is using dynamic pricing to set rates for bags and seat selection. The strategy allows companies to charge flexible rates based on users' browsing behaviour and market demand. A more common pricing strategy among airlines involves rates that change within set boundaries based on variables such as flight routes and dates -- what aviation expert John Gradek calls "variable prices." That pricing strategy does not require a complex algorithm to gauge in real time a passenger's willingness to pay or the collective demand for a particular flight segment. Of course, the use of a range of prices, instead of a single rate, is also aimed at maximizing revenue for airlines.