The maximum possible Oracle server error message number is 32767.

The error messages are not stored in a table. They are stored in files in $ORACLE_HOME/rdbms/mesg/. The first 3 letters of the file name are the oracle facility code; the next 2 letters are a language code; and the extension is either .msg for the text version, or .msb for the binary version. For example the file oraus.msg contains the ORA- server error messages for US English in text format.

For my own error messages I need to use numbers at a range that doesn't clash with the oracle error message range. I assume the range which I could start using is at 100000 and above. Moreover I presume that oracle stores its error messages in some table. Can somebody tell me what table it is?