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OCLC Control Number expansion

WorldCat® continues to grow! OCLC Control Numbers are assigned to WorldCat bibliographic records, including Institution Records. The OCLC Control Number is anticipated to reach one billion sometime after July 1, 2013. At that point, OCLC will increase the length of the OCLC Control Number to accommodate a variable-length number string.

What action should you take? If you use and/or store OCLC MARC bibliographic records and the OCLC Control Number, you will notice a change when the OCLC Control Number
1 billion is reached, sometime after July 1, 2013. You will need to check your institution's systems that use OCLC MARC bibliographic records and the OCLC Control Number. You may need to implement changes to ensure those systems will be able to successfully handle the longer OCLC Control Number.

Sample files for testing

The sample files below can be used to test your systems. The files contain sample MARC bibliographic records with expanded OCLC Control Numbers.

Click the file to download it.

MARC 001 field format

  Format Example
Previous "ocm"+8 digits ocm12345678
Current "ocn"+9 digits ocn123456789
Future "on"+10 or more digits on1234567890 OR  on1234567890123

Note: The "on" prefix will be used for numbers that have 10 or more digits. Lower numbers will continue to use "ocn" or "ocm," as defined above.

Implementation details for MARC field 001

  • If the number is fewer than 8 digits, the format is "ocm" + the number prefixed with 0s to 8 digits + a space at the end

    Example: ocm00000001^

  • If the number is 8 digits, the format is "ocm" + the number + a space at the end

    Example: ocm27344144^

  • If the number is 9 digits, the format is "ocn" + the number

    Example: ocn999001435

  • If the number is 10 or more digits, the format is "on" + the number

    Example: on9990014350


  • "^" designates a space in the examples above. Spaces at the end only occur with prefix "ocm" and not for numbers with other prefixes.
  • Leading zeros are only used with the prefix "ocm" as noted above. They are never used with other prefixes.

Other MARC fields

In the 035 field, the OCLC Control Number is usually stored with the prefix "(OCoLC)," without the "ocm", "ocn" or "on" prefixes, e.g., (OCoLC)1234567890. Most other fields where the OCLC Control Number may be stored, such as in the linking 7XX fields, also usually store the number with the "(OCoLC)" prefix. These fields and subfields are all variable in length, and no special system changes are likely to be needed in order to accommodate the longer OCLC Control Number for those fields.

For more information

Read about OCLC Control Numbers to learn how they are created and how OCLC Batchload services give libraries the ability to match, merge, format and synchronize OCLC Control Numbers between their local systems and WorldCat. To see new OCLC Control Numbers when they are assigned, visit Watch WorldCat Grow.