Question: I want to know how can we know the other users of Oracle 10g on the same system?
Is there any query for that?

Thank you!!!

Answer: 
```
select username
from all_users
/

```

This view doesn't have [much information](http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/statviews_2114.htm#i1593342 "Oracle 10g Reference"). If you need more you will need privileges on its [DBA\_USERS equivalent](http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/statviews_4174.htm#i1628672). As its name suggests, that view requires a DBA level of access.
APC's answer is right. Should you need other users related needs in Oracle:

[Oracle User Schema Owner](http://www.psoug.org/reference/user.html)