We did performance reviews, my boss tells me I'm getting a promotion. "Wow, I didn't expect that, what's my new title?"
After some clarification I learned no title change, no role or responsibility change, but I got a standard of living top up.
The "promotion" meant I was meeting expectations and other people weren't getting standard of living raises anymore. They also cut a bunch of fringe benefits at the same time. Not a good sign.
During his depictions on the shows, at least, O'Brien was in the position of transporter chief, held the rank of chief petty officer, and later became chief of operations on DS9, eventually achieving the rank of senior chief petty officer.
In his original appearances on TNG he had lieutenant's pips, though, and was even referred to as such. At one point he had an ensign's pip instead. He was retconned into being an NCO because apparently the writers were really trying to make his first name functionally be "Chief" for some damn reason.