I have been flying semi regularly to and from ORD for the last 6/7 months, and have been very lucky to get 3 OPUPs during that time (over 13 possible legs). Each of these upgrades was received when I was booked into a 'G' class econ fare, the fares were relatively expensive and booked ~2/3 weeks in advance suggesting a close to full flight. The first was a flexi ticket and I put the upgrade down to this fact plus a seemingly busy flight, the next 2 upgrades were also 'G' class fares but not flexi tickets. The flights were seemingly quite full again so I put the upgrades down to this and my status (I'm platinum) helping plus possibly the simple fact I paid probably more for my econ ticket than most others on the flight. All upgrades were received at the gate (i.e. I got my normal econ boarding pass but at the gate scanning it flashed red and I was issued a business class boarding pass).

As I have read on the BA forum that a lot of these OPUPs result from oversold economy and having space in business and it got me wondering does the 'G' class indicate an oversold class (or close to oversold)? None of my other flights were in 'G' class. I have only a basic understanding of fare classes so it's likely my thinking is off the mark.

Again this is probably just a coincidence but thought I'd share and ask just in case others have similar stories or data points about this (would be interesting in general to get a feel for OPUPs on EI).