I believe that it has been discussed before that oneworld's model is that the operating carrier pays for all benefits; the thought being that oneworld is providing high-value customer leads to the operating carrier. Benefits such as priority security are paid to the airport. The interesting benefit is lounge access: since you can use any oneworld lounge when flying any oneworld airline, they need a way to "settle up" -- it seems from previous posts that carriers have a large amount of leeway, ranging from about $30-40 AA would charge for access to an Admirals Club in the US to $90 for access to the CX F lounge in HKG.

I believe Avios and tier points are also paid for by the operating airline (since the marketing carrier on a non-joint business codeshare usually only gets a commission), but I am less clear on that.