Abstract The Helix Nebula initiative is a partnership between leading European IT-intense scientific research organisations (CERN, EMBL and ESA) and leading IT cloud providers. Its goal is to form a federated Cloud Computing infrastructure that will satisfy the growing demand of scientists for computing power. The concept of the federated cloud requires a standard framework named BlueBox so that current and future cloud providers are able to smoothly interface their system to the existing multi-cloud infrastructure. Section one acts as an introduction to the reader, highlighting the importance of cloud computing in general and at CERN specifically, and provides a brief overview of the Helix Nebula initiative. Section two contains information about the functionality and performance of SlipStream, an interface that has been evaluated as a potential BlueBox solution. Section three contains the analysis of a de facto standard in cloud computing such as the EC2 interface, which is very useful for Helix Nebula and multi-cloud environments in general. Finally, in section 4, you may find listed the key conclusions about SlipStream, based on the evaluation that was carried out along with several other remarks about multi-cloud operations.