The OW rules are as follows
***Extra baggage allowance for Sapphire frequent flyers
As a Sapphire frequent flyer, the following special checked baggage privileges will apply when you fly on
oneworld airlines:
- On international or domestic itineraries using the baggage allowance "weight" system - 15 kgs in addition to the ticketed Economy Class baggage allowance.
- On international itineraries, that include domestic sectors, using the baggage allowance “piece” system – one additional bag*, weighing up to 23kgs, up to a maximum of two pieces.
- On purely domestic itineraries, using the baggage allowance "piece" system, for tickets with no ticketed baggage entitlement - the assurance of one piece of checked baggage, weighing up to 23 kgs.
Customers travelling in First and Business Class cabins will, in most cases, receive an even greater free checked baggage allowance.
Note: This benefit is not available on British Airways’ 'Hand Baggage Only/Basic' fares.
*In accordance with the individual policy of the
oneworld airline operating the flight. **Priority baggage handling is not currently available on flights operated by British Airways.
IB follows them, for instance, giving you an extra piece when flying in Economy (even in Basic Economy, which BA does not do). But there is no OW-wide rule for overweight fees.
Of course, very often the check-in staff feels more generous and lets a 25 kg bag go by, but it is not the rule.