Depending on class of travel and which airline you are flying you may not get access to all OW lounges. Example, as a oneworld Emerald card holder you should get access to all first class lounges. However at LHR & JFK, unless you are flying Concorde or BA First you will not have access to the Concorde room (tried this recently when flying QF in first from JFK to LAX). BA has separate First lounges at LHR & JFK to which other passengers are directed. Another case in point is LAX. BA & QF have now allocated one of the lounges to be only for first class passengers. When I was there recently some J class passengers who were QF Platinum were turned away and told there was another lounge for Emerald status card holders (was one of the old J lounges I believe).