An Ocean Developers License is legally required to create Ocean plug-ins. The licensing of the plug-in is the responsibility of the plug-in developer and the Ocean API provides classes to help with the licensing.
An Ocean Developers License provides access to all licensable modules of the Petrel and Studio platforms. When running Petrel using an Ocean Developers License the windows will be watermarked indicating that the Ocean Developers License is in use. If a Petrel project is saved when running under an Ocean Developers License the project will be tainted, with appropriate warning, and will not be able to be opened when running Petrel with a production Petrel license.