What is the secret to upgrading on Code Share flights? I recently few from MUC to LAX on UA flight, operated by LUF. I called for an upgrade (twice) and both times was told that because it had a UA flight number, I could not upgrade on the LUF plane. They told me if I had booked a LUF flight, then I could have upgraded. I then asked at the LUF gate in MUC if I could upgrade. They told me a different story. They said that it didn�t matter who I booked through, I couldn�t upgrade because the airlines do not allow each other access to the mileage accounts of the others customers. He said there is no way they could get the miles to upgrade. He said the only way to upgrade is to have a paper �voucher� from United that was purchased with miles that would be given to LUF to upgrade.

So, that is the true story? What is the code for upgrading on code share flights?

It's no secret - never book a codeshare. (It's FT Rule #2.)

You can only upgrade ahead of time, you can use miles, but only if you booked a Y or B fare, and not on a codeshare. On the day of departure, you can only upgrade with a paper SWU on a qualifying fare.

Yup ^ (and this is right after F/t rule #1 which is if you don't like your answer, hang up and call back )

True, although the OP would have been told the same thing.

what about upgrading CO domestic flights sold as UA codeshares? I'm doing one this week and still in the dark about the reciprocal upgrade system.