can anyone explain this regulation issue?

[gain]

got 14.76V on the top rail and -15.21V on the bottom. stays rock steady at those values with increasing loads too. the opamp i'm driving it with doesn't seem to mind, just was curious why it was occurring.

schematic attached.

thanks

[lineup]

There is a production variation in most components.
Within a bunch of same transistors produced the current gain can go from 100-700!
1% resistors nominal 1000 Ohm ( 1 k ) can range 990 - 1010 Ohm.
5 % resistors can be anything from 950 - 1050 Ohm.

Same for chips like regulators.
The variation from nominal 15.00 for you is 14.76V and -15.21V.
Which actually is very small: -1.6% and +1.4%

And as you have discovered the opamp does not mind a bit

http://www.national.com/ds/LM/LM7512C.pdf (positive regulators)
http://www.national.com/ds/LM/LM7905.pdf (negative regulators)
National LM7815 datasheet gives these tolerance facts:
Min 14.25V and Max 15.75. This is +-5% accuracy.
Most exemplars however will be closer to 15.00, than this 5% variation.

[gain]

thanks lineup!

makes perfect sense.