As per the oneworld website:
Lounge Access by Tier Status
When travelling on any oneworld member airline, any customer with Sapphire tier status is welcome (with one guest travelling on a flight operated and marketed by a oneworld airline) at any oneworld airlines' pre-flight Business Class and frequent flyer lounges regardless of class of travel.
I was travelling in Y on AA as a OW Sapphire (Qantas Gold) from IAD to LAX recently and was refused entry to the BA lounge at IAD despite me quoting the above. I was told that the local airport rules dictated that I use the (inferior) AA lounge as I was flying on AA. I was only allowed entry to the BA lounge if I was travelling BA. This seems to be against the oneworld rules
Was I wrongly denied? Comments please.