Dustin McQuaywrote a review of CamelBak Octane 18X Hydration Pack - 1281cu in on November 22, 2011
I took this pack on a week long trail running adventure in Guatemala and LOVED it. It was big enough to take water for almost a whole day every day. I only had to refill on particularly long days when we were out over 8 hours or so. I generally carried an electrolyte bottled drink in the bag to supplement the water.
I was able to carry the full bladder, the extra bottle of electrolyte, food for the day and an extra layer and still didn't have to open the expandable compartment (my extra layer was VERY thin though).
When the bladder is completely full, you will find that it moves around a bit while you run. But, I was still able to run with it.
I read a review that said the straps would slip. Even with it fully loaded, that did no happen to me.
The pack is very comfortable. It did not rub me weird in any places.
Love this pack. Recommend highly.
I was on this adventure if you want more details: http://www.mayanrunningadventure.com/