Looking at some European flights for next week and the seat maps suggest there is some chance of op-ups (half full J + nearly full basic Y seats + nearly empty preferred/EC seats). However the same flights are a fair deal cheaper sold on KL codes rather than DL codes. Does anyone have experience getting an op-up on a KL-coded (or other partner coded), DL-operated flight? Any idea where that would put me in the priority order? Trying to decide whether it is worth some extra $ for a better chance of the op-up.

That looks like pretty slim chance for op-up. You need completely full Y cabin, including preferred/EC seats. Furthermore, seatmaps are nearly useless for predicting op-up. You need to look at fare buckets.

I wouldn't pay much extra in an attempt to improve OPUP chances. Who gets the OPUP is the GA's discretion, although top tier elites tend to be considered first. If it's a DL operated flight from AMS, remember that KLM does ground handling for DL, so KLM agents will be handling the OPUPs. They might or might not follow normal DL procedures.

I agree, and understand, but the seat map situation I described is still a useful indicator, because with all regular Y seats taken, that likely means there are some number of passengers holding tickets but no seat assignments. Further, those passengers are not elite, or they'd already have preferred seats at least, and likely EC seats if PM/DM, so they are not competing with me for any potential op-up. At the gate, it is entirely possible that there will be enough empty preferred/EC seats to give them to all seatless non-status pax and no one will need to be op-upped, but I have definitely gotten op-ups before with a seat map that looked very similar. Indeed, though a 100% assigned coach seat map could be another decent indication of possible op-ups, those op-ups would be very unlikely to go to a GM, since a fully assigned seat map means there are lots of elites on board, some share of which are likely to be PM/DM.

Fare buckets can also be useful, but again in my experience Delta is not as transparent about oversold/op-up situations in their fare buckets as some carriers are. (I think I have heard, though I may be making this up, that some carriers will even show negative numbers in fare buckets when oversold? I certainly have never seen this on Delta.) On a flight a few weeks ago where I was op-upped, the Y fare bucket and a few below it were still showing positive availability as I waited at the gate despite coach being oversold, presumably because Delta was still willing to sell tickets and op-up as necessary (and BE did go out with some empty seats).

But in any case, my question has become moot, since the cheaper KL fare disappeared while I debated.

I don't think you're off on this, colerc. On my two most recent op-ups the seat map looked pretty similar to the one you're describing. I also have a flight coming up that looks that way, and am crossing my fingers. Obviously it's impossible to know, but as another GM flying in and out of NYC I can say that my experiences line up with yours.

Not going to happen. Not. Safe travels.

Maybe, maybe not. A lot of us have gotten op-ups this summer on flights full in Y and undersold in J. I noticed similar phenomena, although until the flights got down around Y3, I didn't get my hopes up. That said, I got one on a KL-operated flight that was Y3 the last time I checked in the lounge.