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OCLC Support

035 field and OCLC control numbers

Find out how data sync processing uses preprocessing routines to map existing OCLC control numbers to field 035 $a, prefixed with (OCoLC).

Data sync uses OCLC control numbers in your records in the following ways:

  • Match WorldCat records
  • Link local records from local systems to WorldCat records

Because the format of OCLC control numbers has changed over many years and many local systems remove it or put it in a field other than 035, OCLC batch services uses preprocessing routines to map existing OCLC control numbers to field 035 $a, prefixed with (OCoLC).

The following table describes the changes in OCLC control numbers formatting and location over time. Records can contain any of these formats and locations for the OCLC number.

Descripción Format Ejemplos
The OCLC control number in field 001 is prefixed by ocm, ocn, or on.

OCLC numbers 1 through 99999999:

  • Have an ocm prefix
  • Composed of 8 digits, right justified, with leading zeros
  • Followed by a blank

OCLC numbers 100000000 and higher:

  • Have an ocn prefix
  • Composed of 9 digits

OCLC numbers 1000000000 and higher:

  • Have an on prefix
  • Composed of 10 or more digits


The OCLC control number in field 035 ‡a is prefixed by (OCoLC). OCLC number is a variable-length numeric string with leading zeros for numbers with less than 8 digits and no leading zeros for those with 8 or more digits. (OCoLC)198765401


 Note: Field 019 contains the OCLC control number of a deleted or merged record replaced by the current one.