The official website of Oreimo confirmed that there would be eight volumes of their respective BluRay/DVD release, and every volume contains two episodes. Making volumes 7 and 8 having two extra episodes each!
It was listed that the TV run will have 12 episodes ending with Ore no Imōto no Jinsei Sōdan ga Kore de Owaru Wake ga Nai -Good End-. According to an unconfirmed rumor, on a live event that happened on December 5, Aniplex announced that the series end like what the last part of it, will be the "good end" of the series. But as we all know, the series has eroge and visual novel references, in short there would be a true end.
Accordingly, a different episode 11 will air online which will branch out from the TV series run. Which will be followed by episodes 12-15, with the 15 episode being called the "true end."
The seventh and eighth volumes will be shipped on June 22 and July 27, 2011.
Source: ANN, MyAnimeList