select current_utilization, limit_value
from v$resource_limit
where resource_name='sessions';

current_utilization, limit_value
177, 987

select max(a.value) as highest_open_cur, p.value as max_open_cur
  from v$sesstat a, v$statname b, v$parameter p
  where a.statistic# = b.statistic#
  and b.name = 'opened cursors current'
  and p.name= 'open_cursors'
  group by p.value;

highest_open_cur, max_open_cur
  241, 4000

Oracle Database 12c Standard Edition Release 12.2.0.1.0 - 64bit Production
TNS for 64-bit Windows: Version 12.2.0.1.0 - Production

Inter® Xeon® Gold 6126 CPU @2.6 Ghz
4 Sockets, 4 Virtual Processors
Java HotSpot(TM) 64-Bit Server VM (build 25.162-b12, mixed mode)
HEAP=-Xms20G -Xmx20G -XX:MaxMetaspaceSize=128m
Windows Server 2016 Standard