Originally Posted by carlosdca

You already got an answer above.
Another example JFK-LHR-TXL, where JFK-LHR is on AA and LHR-TXL is on BA but LHR-TXL will be sold with a AA flight number.
But, you won't be able to buy only LHR-TXL as an AA codeshare flight, it will be a BA marketed and operated flight.

So no, I don't think you will be able to buy a AA codeshare originating in Europe and with Europe as final destination.