Actually, Dak, we need more thorough DD than that. It depends on the size of the bottle and the company. There can be as few as 6 and as many as 32. Typical of 20 oz bottles IS 24, but they commonly exist in 16, 20, 28 and 32 per sizes. I don't know that anyone has released qty per case. At least, I haven't seen it anywhere.
Now, if you're talking wine or spirits, yes, 12 would be pretty standard, though they come as little as 4 and as many as 20.