Marco Polo elite members are given extra allowances though not oneworld elite members.

MPO Silver get an extra 10kg excess allowance, Gold gets 15kg and Diamond members get 20kg extra.

CX may sometimes waive up to 10kg over if you're not a MPO but are travelling in Business or First Class.

But if you're on part of a RTW itinerary, the piece system is implemented and thus you are permitted to carry 2 pieces of 32kg each.