The merger saga between LAN of Chile and TAM of Brazil has now been going on for two years. The merger was finally approved at the end of June and the new airline group LATAM was born.
The problem here is that the LAN is a member of oneworld alliance and the TAM is a member of competing Star Alliance. It is widely known that the combined airline will choose oneworld as their alliance. In order for the competing authorities to approve the merger, the airlines had to agree that they cannot be in the same alliance as the recently Star Alliance joined AviancaTaca.
LAN is an interesting airline. They have their base in Chile, but subsidiaries all over the South America; LAN Peru, LAN Argentina, LAN Colombia, and LAN Ecuador.
TAM only has one subsidiary TAM Mercosur in Paraguay.
For now, both of the airlines will continue to operate within their alliances. LATAM has not informed yet, when the TAM will withdraw from the Star Alliance, but the process will likely take months. I would say that the end of 2012 would be a logical choice, but it could happen sooner as well.
You will likely see LAN codes on most of the TAM flights and vice versa. If you are collecting miles on any of the oneworld programs, you won’t get any benefits or miles on LAN flights that are operated by TAM. The same goes for TAM flights that are operated by LAN.
There are now, however, benefits for LAN elite members that take TAM flights and vice versa. You can read more about these benefits and other merger related information here.
I have flown both airlines many times, although TAM only domestically within Brazil. I have few flights coming in on LAN on September in business class; Auckland to Santiago, Santiago to Easter Islands, and Easter Islands to Papeete.