Op Amp Power Supply Consideration
There is current that flows from the positive supply to the minus supply. Most op-amps do not have a ground pin. Whatever current the op-amp itself requires will thus be supplied by both supplies. Usually this is only part of the whole picture though since the op-amp by itself won't do anything useful. 

The load resistors (and resistors associated with the feedback network) are often to ground rather than to a supply, so the current will flow from either the positive supply or the negative supply to ground. If you only drive the op-amp output (say) positive and there is a heavy load to ground, you may not need as much capacity on the negative supply. You won't find the numbers on the op-amp datasheet- you will have to analyze the circuit. 

Generally though you will be safer with the same rating on both supplies. Note that SPICE models of op-amps may not bother to model the op-amp supply currents accurately.