OCLC Control Number

The OCLC Control Number is a unique, sequentially assigned number associated with a record in WorldCat. The number is included in a WorldCat® record when the record is created. The OCLC Control Number enables successful implementation and use of many OCLC products and services, including WorldCat Discovery and WorldShare Collection Manager.

The OCLC Control Number is used to:

  • Facilitate visibility of information from library catalogs on the Web
    • Enable communication between WorldCat and your local system to display local location, circulation status and availability information for items in your OPAC
    • Provide users with fulfillment options, such as placing a hold or submitting an ILL request
  • Create the match point between WorldCat Local or WorldCat Navigator and your local system for retrieving real-time availability and for placing local or consortially held requests
  • Synchronize WorldCat data and CONTENTdm® data while using Connexion®
  • Enable "deep" links from WorldCat.org to your library catalog via the WorldCat Registry to expose your WorldCat holdings to users via the Web
  • Facilitate searching by entering the OCLC Control Number in WorldCat.org™ advanced search to find an item
  • Search Google Books to reference a particular edition; see OCLC numbers as manifestation identifiers

OCLC encourages the use of the OCLC Control Number in any appropriate library application in which it can be treated as if it is in the public domain.

How OCLC creates the OCLC Control Numbers

OCLC systems, including Connexion, WorldCat cataloging partners collections (formerly WorldCat Cataloging Partners), CatExpress and WorldCat data sync collections (formerly OCLC Batchload services), assign the OCLC Control Number to each bibliographic record input into the database as the records are entered.

OCLC Control Numbers in MARC records

Bibliographic records output from OCLC systems, including Connexion, cataloging partner collections and CatExpress®, contain the OCLC Control Number. WorldCat Local supports one custom OCLC Control Number prefix. The "ocm" or "ocn" prefixes are considered a single prefix.

The OCLC Control Number can be found in fields 001, 019, and 035 as follows.

  • On records created 12 November 2006 and before, field 001 contains the OCLC Control Number.
  • On records created after 12 November 2006, field 035 contains the OCLC Control Number.
  • Field 019 contains the OCLC Control Number of a deleted or merged record replaced by the current one.
  • In Field 001, the OCLC Control Number is prefixed by "ocm" or "ocn" or "on."
  • In Field 035, $a, the OCLC Control Number is prefixed by "OCoLC."


Here are the standard formats in which the OCLC Control Number is output from OCLC cataloging services.

001 field (12 characters)

OCLC numbers 1 through 99999999:

  • ocm prefix
  • OCLC Control Number, 8 digits, right-justified with leading zeros
  • blank

    Example: ocm00012345

OCLC numbers 100000000 and higher:

  • ocn prefix
  • OCLC Control Number, 9 digits

    Example: ocn123456789

OCLC numbers 1000000000 and higher:

  • on prefix
  • OCLC Control Number, 10 or more digits

    Example: on1345345345

035 field

OCLC Control Number is a variable-length numeric string with no leading zeros and preceded by "(OCoLC)."

Example: (OCoLC)198765401

WorldCat data sync collections synchronize your local system and WorldCat

Data sync collections give you the ability to match, merge, format and synchronize OCLC Control Numbers between your local system and WorldCat.

Initial synchronization and ongoing maintenance of OCLC Control Numbers within your local system is necessary when implementing WorldCat Local or WorldCat Navigator, as "consistently indexed" OCLC Control Numbers are required for WorldCat Local and WorldCat Navigator to work.

"Consistently indexed" means that, using the standard format, the OCLC Control Number is placed in the same field of all MARC records in a library's local system, and the number is prefixed in a consistent manner. OCLC supports one custom prefix scheme — ocm, ocn or OCoLC. The OCLC Control Numbers must also be either consistently padded with leading zeros or unpadded.

For more information, visit the WorldShare Collection Manager website, read the data sync collection documentation guide or contact OCLC.

There are 3 options available for obtaining OCLC Control Numbers from data sync collections.

  1. The Cross Reference (XREF) Report

    Used to match and merge the OCLC Control Numbers into the bibliographic records in your local system

  2. Your records returned with the OCLC Control Number

    Merges the matching OCLC Control Number back into the record that you send to OCLC for processing

  3. Full OCLC-MARC records

    A file of matching OCLC-MARC records—containing the OCLC Control Number—can be returned to your institution