Memory exhasted Problem in php

Hello Experts,

I'm getting this kind of error each and every long in time
"Fatal error: Allowed memory size of 16777216 bytes exhausted (tried to allocate 35 bytes) in file/path"
I hope you experts helps us,

I tried by unsetting the Variables and by increasing the memory size through the configurations and still i am facing the Problem
Thanks,
Parameshwara