Section 22.214.171.124 of the J2EE 1.3 specification mandates explicit support for the bundling of dependent .jar files via the Extension Mechanism Architecture (see the References section). Application servers must load dependent .jar files listed in the Manifest Class-Path entry of a primary .jar file (typically an EJB .jar). This requirement is not mandated for .ear or .war files.
As of Service Pack 2 of WebLogic 6.1 (WebLogic issue 056911 -- see the References section below), .jar files listed in a Manifest Class-Path entry are loaded by the application's EJB class loader. This applies to Manifest Class-Path entries found in EJB .jar files and web application .war files within the .ear. Note that the Manifest Class-Path approach is only supported when deploying components within an .ear.