I couldn't figure out why there was so much discrepancy on the water volume. Half say 70oz, and half say 50oz. The bag will acutally hold 70oz, but you will lose most of that as it drips down your back. There isn't a gasket on the opening.
I bought this for my first 50K ultra. The pack is okay for shorter runs (1/2 marathons) when you don't need to fill the bag. It doesn't have any place to put gels except the back, so you would have to take off the pack. I am donating this one to my kids for our short trail adventures. Bought an Ultimate Direction Wisp and couldn't be happier.