can't execute opatch even I'm in the oinstall group with -rwx–x—

I’m in $ORACLE_HOME/OPatch directory and
i type opatch
then it response: -bash: opatch: command not found
if i do ./opatch
then it response: /bin/sh: ./opatch: Permission denied

opatch ls -l shows

-rwx–x— so for group user which is oinstall, it should have execute right.

and

id -g does show me in the oinstall group.

So why I can’t execute opatch in this case?