When to use OSB & BPEL?

Use OSB for:

• Endpoint routing (providing location transparency) so that we do not care about the physical location of the endpoint.
• Endpoint abstraction (interface transparency) so that we do not care about the exact data formats required by the endpoint because the OSB will take care of transformations.
• Load balancing so that we do not care about which of multiple service implementations will actually service a request. 
• Throttling so that we do not care about how use of services is restricted.  
• Enrichment so that we do not care about how additional data is provided to the request to match the expected request and response formats.
• Simple synchronous composition so that we do not care if our abstract service call is actually made up of two or more physical service calls.
• Protocol conversion so that we do not care what physical transports are being used.
• Sync/async abstraction so that we can treat services as fire and forget or query response according to the needs of the client.

Use BPEL for:

• Complex composition of parallel flows that involve more than a couple of services.
• Long running compositions that may run for minutes, hours or days.
• Asynchronous compositions that require correlation of requests and responses.
• Process abstraction that enables us to track processes and their interactions with multiple services.
• Human workflow

Related blog topics:

Exposing BPEL thru OSB

BPEL Dehydration Store - Detailed

Exposing Ora BPEL processes as Web services in OSB layer

Oracle BPEL PM - Components