Alternative Database Management Systems

I am trying to get WordPress approved in our organization.
MySQL is stated as being required.
However, they currently do not have MYSQL approved. It takes months or more to get products approved.
Is there any other database system that can be used with the current WordPress Release? Such as , PostgreSQL, Microsoft SQL Server, or Oracle?
Or is there major modifications that need to be made?
Getting WordPress in our organization may potentially spawn off dozens of instances throughout the organization.