Here's how to find out for sure:

1. Make sure the flight is zeroed out in all classes.
2. Locate the aircraft type, and identify the number of seats (n)
3. Get someone at CO to spill by how many the flight is overbooked (o)
4. To validate, contact each passenger and count the number you can get to promise to make the flight (p)
5. If p - n > 0, then you got yourself an oversale.

Seriously, though, there's no way to predict. They overbook the flight by the amount of pax they think will no show or cancel. If they get this wrong, they either leave money on the table (they didn't sell enough seats), or they end up bumping people (they sold too many). In reality, CO knows the history of the flight, the season, etc., so they hold all the cards and are really good at this.

In my experience, many oversales are a function of something wacky happening (e.g., flight cancelling and a mad rush of rebookings), and many "potential bumps that look good" often fail because of something unforeseen (e.g., traffic on the freeway, misconnects from a delayed inbound flight, a long line a customs causing misconnects, etc.).

My gf had one of these "potential bumps that look good" until the flight went mechanical and delayed 3 hours. They started rebooking people onto other routes, essentially resolving the oversold situation.

Just get there, volunteer, and hope for the best.