select value sess_mem  
    from v$sesstat s, v$statname n  
   where s.statistic# = n.statistic#  
    and  n.name = 'session uga memory'  
    and  s.sid  = &sid;

select value sess_max_mem  
    from v$sesstat s, v$statname n  
   where s.statistic# = n.statistic#  
    and  n.name = 'session uga memory max'  
    and  s.sid  = &sid;

 select sum(value) all_sess_mem  
    from v$sesstat s, v$statname n  
   where s.statistic# = n.statistic#  
    and  n.name = 'session uga memory max'; 
