List sudo users in centos

How do I list all sudo users at CentOS server?

There are many groups(root, wheel, adm etc) at server, and have users in it. I am looking an easy way/command to find users in all groups who have sudo access.

Note: My user also have sudo access. And I am using 64-bit CentOS release 5.2 (Final).

Try this:

for USER in `cut -d: -f1 /etc/passwd`
do
  sudo -U $USER -l
done

What is wrong with sudo cat /etc/sudoers and maybe getent group <groupname> to get usernames of group members?

When adding users with sudo permissions on centos7, its advised to add them to the wheel usergroup which by default has sudo permissions with

sudo gpasswd -a <user_name> wheel

Following @Sven 's answer, does the trick for centos7.

getent group wheel