Hello,
What modifier is added in oracles concentration checks?
In nearly all cases, you use your primary spellcasting stat for Concentration checks, which is Charisma for an oracle (you use Charisma in the case of spell-like abilities that don't say to do otherwise).
If you have multiple classes or abilities that grant Concentration checks (such as a cleric/wizard for example) you either keep each class' Concentration check modifiers separate, or you use the higher one. Official stat blocks have done it both ways, and which method is RAI and RAW is unclear at the moment.
Thank you, Ravingdork.