Both Qatar Airways and SriLankan Airlines are expected to join the Oneworld alliance sometime in the late 2013/early 2014. The joining dates for both of the airlines have not been confirmed yet.
Now, you can, however, start using these two airlines on Oneworld alliance’s Global Explorer fares. At the same time, the gulf carrier, Gulf Air has withdrawn its participation on these fares. Gulf Air has never been member elect or future member of the alliance. You can read the press release about this announcement here.
Thing to note is that even these two airlines now participate to these Global Explorer Round The World fares it doesn’t mean that you would earn any elite or award miles on these two airlines on Oneworld alliance member airlines’ frequent flier programs before they have officially joined the alliance.
This was an expected step for both of the airlines joining the alliance. You just have to be very careful with these two airlines IF you are planning to credit the flights to i.e. AA’s or BA’s program. The official joining dates of these airlines have not been confirmed. It is likely that you don’t earn any miles before they are officially part of the alliance.