manual vs. automatic

[osmoq]

If there is already a thread about this secifically, can someone point me to it? I looked, but couldn't find one.
From browsing the threads, it seems like peole with manual transmission get really good gas mileage, but I've seen some reports with the automatic that aren't as good. I'm trying to figure out if this is a coincidence based on what I've seen. Can people post whether they have a manual or automatic and their average mpg? Or if anyone knows real-world mpg manual/auto comparison reports, that would be great.
I ask because I was planning on getting a manual, but I'm looking at a specific automatic one, now, and I want to make sure I'll get the max gas mileage because that's one of the main reasons I want the car.

Thanks!