Differentiated Services provide a scalable Quality of Service Concept for the Internet. It allows differentiating service classes which may be treated individually. The data arising between two neighboring network providers is regulated by Service Level Agreements (SLA). The use of static SLAs lacks flexibility. With the introduction of Bandwidth Brokers a concept was provided enabling a dynamic Differentiated Services environment. Bandwidth Brokers automatically negotiate and set up SLAs. However, this may still fail if there are bottlenecks in the network that may lead to congestion. This paper extends an existing scalable Bandwidth Broker concept for handling congestion in dynamic Differentiated Services networks. Our mechanism applies in contrast to any previous approach a dynamic overprovisioning and is able to handle different levels of congestion situations. With help of this dynamic overprovisioning we are able to maximize the utilization. The merits of this new concept are shown in simulation.