There are five Permanent Private Halls (PPHs) at Oxford admitting undergraduates.
PPHs tend to be smaller than colleges, and offer fewer subjects. (See Which PPHs offer my course?) However, students at PPHs are members of the University just like students at colleges, and have access to exactly the same University facilities and activities. Regent’s Park is the largest PPH, and accepts applications from students of any age. Until now St Benet’s Hall has admitted only male undergraduates but will accept applications from both male and female applicants - of any age - this year, for entry in 2016 or deferred entry in 2017. Blackfriars, St Stephen’s House and Wycliffe Hall only accept mature students. ("Mature student" means 21 or over at the start of October in your first year.)