I've done some heavy DTracing of this, and it doesn't appear to be very high. Commonly ~5 microseconds per call (it's actually two ETS lookups). That is BTW, better than the average dict lookup .  There is a plan to possibly optimize this further through the app_helper:get_env(). I would suggest to always prefer that interface to a raw application:get_env() to take advantage of any future optimizations.