The Oracle Database is available in a variety of editions, each differing in both functionality and target audience.

The premier edition is Enterprise Edition (EE), which retails at 40,000 dollars per processor (list price from Oracle Store as of October 15th, 2007). Enterprise Edition scales to the largest servers available and contains no limit on processor count, storage size, or additional options. Features like partitioning, replication, and advanced monitoring are additional cost options only available for Enterprise Edition.

The mid range edition is Standard Edition (SE), which retails at 15,000 dollars per processor. As of October 15th, 2007, Standard Edition is limited to 4 processor sockets. However, because the Real Application Clusters option is available free of charge with this edition, multiple Standard Edition installations can be spread across several clustered servers. Additional cost options - with the exception of RAC - are not available with this edition.

The small-business version is named Standard Edition One (SEO), and retails at just under 5,000 dollars per processor. It is licensable on single servers with only one or two processor sockets. Similar to Standard Edition, additional cost options are also unavailable with this edition.

There is a cost-free edition,Oracle Database Express Edition (XE) available for both Linux and Windows. While based on the same source code as Enterprise Edition, it is limited to a single processor core, 4GB of user data storage, and 1GB of memory. This edition is targeted toward developers, ISV's, and small installations which might otherwise choose, for example, the LAMP stack. Apart from the OTN community-oriented support forums, this edition is unsupported. As such, patches and additional cost options are not available for it.

Finally, there is a "Personal Edition", which is licenced for a Named User only. With the exception of RAC and management pack options, Personal Edition contains all the functionality of Enterprise Edition; making it well-suited for consultants, professional developers, and hobbyists. Similarly,it is the cheapest supported edition of Oracle.

The details of the Editions can be found in the Licensing 'book' in the appropriate documentation set. For 11g, that document can be accessed here.