can airline join multiple alliances?

Just a general question:

Is it possible for an airline to join multiple alliances?
for example SkyTeam and Oneworld?
Does it happen?

No, why would partner airlines of one alliance allow that? To promote loyalty amongst alliance partners is the whole point.

thanks for your reply. As far as I understand, it isn't possible for an airline to be a direct member of multiple alliances.

On the wikipedia page of Oneworld, there is an table with all members of Oneworld. http://en.wikipedia.org/wiki/Oneworld

Here you see member airlines, but also member affiliates and non-member affiliates.

As far as I understand, all these airlines in all columns, are part of the Oneworld network.

Is it possible for an airline in the second or third column to be part of multiple alliance networks?

All those airlines are usually regional airlines owned by the main airline, so it's quite unlikely they can join another alliance.
Member affiliates are part of oneworld
Non member affiliates are not part of oneworld but owned by a oneworld airline

No they are not all OneWorld. The Wikipedia page is not well done. The meaning of the word "affiliates" is not well defined in Wikipedia. Look at www.OneWorld.com.

1. Would make zero sense from a business perspective since the entire purpose of an alliance is to supply "seamless" transportation between more locations than one carrier can handle.

2. No competition regulator would allow it even if one of the alliances were dumb enough to want it.

Some airlines have partners in different alliances. Alaska Air has OneWorld and SkyTeam partners, although they themselves are not in an alliance.

And many alliance-member airlines have codeshare partners from opposing alliances, e.g. Qantas and South African, CX and Air New Zealand.

the only airlines i can think of that are affiliates that are in more then one alliance are the US regional carriers Skywest operates contract flights for American, Delta and United. technically they are not in an alliance except for the flights operated under contracts for those alliances

member affiliates: including those airlines are operating on a franchise agreement of a member airline (i.e. Comair in South Africa), a wholly or partly owned subsidiaries of the member airlines that participate on oneworld membership agreement (i.e. Dragon Air of Cathay Pacific). and a separate brand that belongs to the member airlines (i.e. American Eagle of American Airlines)

non-member affiliates: including those airlines are operating on behave of member airlines but does not provide oneworld service (i.e. Ryukyu Air Commuter for JAL) and those are wholly owned or partially owned by member airlines but does not participate in alliance (i.e. Vueling and jetstar).

For member affiliate, they are oneworld members and they are not allowed to be in another alliance. for non-member affiliate, they are not in oneworld. If they are operating on their own they may develop bilateral relationship with other alliances, but not sure if it is forbidden by oneworld contract of the parent companies.

In SkyWest's case, they are neither a member affiliate or non-member affiliate. They are a sort of a flight lease company and provide aircraft and operations based on member airlines' contracts and requirement. the operation is considered as part of the member airline's network.

FJ is owned by Qantas, but is an affiliate with almost everyone for codeshares and points earn/spend. They even... "have relations" to/from Alaska Air. FJ gets around.

Not really. From Wikipedia:

Air Pacific is owned by the Fijian government (51%), the Australian flag-carrier Qantas (46.32%), and Air New Zealand and the governments of Kiribati, Tonga, Nauru and Samoa each hold minor stakes.

I thought the percentages were the other way around. My mistake.

Alaska Airlines has parnership with Delta and American.

Yes, however it is not a member of Skyteam or Oneworld.