A REGION parameter on an EXEC statement, overrides the REGION parameter on the JOB statement.

A REGION parameter on an EXEC statement, limits the space available for that step, but will never exceed the REGION on the JOB statement.

A REGION parameter on an EXEC statement, is only taken into consideration if there is no REGION parameter on the JOB statement.

The sum of all REGION parameters on EXEC statements, must be equal to the REGION parameter on the JOB statement.