Originally Posted by
aspire
Hi. I have OneWorld Emerald (through AirBerlin gold), and I'm an AAdvantage member but do not have status with American. I will be flying SEA-ORD on American, in economy, this Friday. Are there any lounges in Sea-Tac that I will be able to access through my OW status? Thanks!
Originally Posted by
SJC AA
There's a BA lounge with very limited hours that is not at all convenient to the AA gates. They may or may not let you in (BA is notorious for playing games with lounge rules). Otherwise, it's a fairly nice airport so not a tragedy if you can't get lounge access.
SJC AA sums it up pretty nicely.

But just to add a little more detail... The BA lounge opens at 3pm and closes after the last BA flight leaves. It's all the way over at the S gates, in the same lounge complex/hallway as a Delta lounge and maybe another a lounge. (Sorry, it's been a while since I've been there.)
In theory this is an official BA lounge, so oneworld lounge rules apply (i.e., as a non-AA oneworld elite, you should have access to oneworld lounges when departing on a oneworld marketed/operated flight).