there are many considerations that come into play when planning to tanker fuel. obviously $$$ savings is a major consideration, especially as fuel prices are climbing rapidly. we often tanker into stations where the fuel companies have increased prices dramatically as a shot across their bows. this has sometimes led to fuel prices dropping again.....so then we don't tanker. we also have to deal with extremes in wx conditions - don't want to tanker into/out of airports where adding wt to an aircraft becomes an issue - short rwys / high temps / snow&ice / heavy rain / tstms, flap-settings, heavy braking, etc. another factor is engine wear and tear.....we may save some money by tankering, but if having to use increased thrust to get out of dodge, any savings could be blown out of the tail pipe and/or increased maint costs. other factors may involve enroute wx - if you tanker to the gills and can only step climb, you may not be able to top enroute turbc. another factor is that if you tanker, you may not be able to get optimal flt levels - example, from minneapolis southbound, tankering may restrict you to fl330 initially - this will put you in direct conflict with east-west flow into ord, so you end up at fl290 for the first 45 mins of flt, whereas not tankering will let you climb straight to fl370, above the flow into/out of ord. so, many parts to the equation, and we need to make judicious decisions about this every day. it may may perfect sense to tanker one day, but the next day on the same flight, conditions may dictate otherwise. i could save my salary by tankering everyday, but have to temper this economic aspect with safety, which must come first.