Recently I needed to create a user in Oracle11g database and I was surprised that for other people following expression works well:

CREATE USER name IDENTIFIED BY password
But I'm constantly getting ORA-00922: missing or invalid option error. Quoting the password solves the problem, so following expression works fine: 

CREATE USER name IDENTIFIED BY "password"

It turned out that for password which contain only digits or start with a letter quotes aren't needed, so first expression works fine. But if the password starts with digit then quotes are required. So 123456, qwerty and asdf1234 don't need quotes, while "1234qwer" or "2asdf" should be quoted.