You don't say what your status is?
As a oneworld status benefit only oneworld emerald is provided an additional baggage benefit.
From oneworld.com:
Extra baggage allowance
As an Emerald frequent flyer you can check in one additional bag for free in addition to your ticketed baggage allowance when you fly on oneworld airlines. If your ticket mentions a weight allowance, you can check in an extra 20kgs (44lbs). (This benefit is not available on British Airways 'Hand Baggage Only' fares on select short-haul routes.)
If you aren't emerald (AA Executive Platinum) any additional benefit will be up to the individual airline, I would not expect them all (especially AB) to be as generous as AA. You may want to check the forums for the airlines here on FT and the individual airline websites.