Second Season of Highschool DxD Announced [Update Sep 6]

The second season of Highschool DxD was announced in the OVA bundled with the 13th volume of the original novel.

Highschoold DxD official website

Source: Screenshot of the announcement

Update Sep 6
Acccording to Fujimishobo, a new OVA of Highschool DxD was announced to be released in May 2013. It will be the unaired episode 14 of the first season and will be bundled with the 15th volume of the novel.

Source: Scan of the notice

Highschool DxD Dai 2-ki on MAL