Write down the copyright date and ISBN number of the World Book Encyclopedia you own. This information can be found after the title page on any volume. Also write down the volume number you are missing.
Contact a World Book customer service sales representative by calling 1-800-338-8382. World Book does not offer single volume purchases online. The representative has to verify the availability of the particular volume.
Pay for the volume over the phone. Replacement volumes, when available, are $50 (as of March 2011) regardless of publication year. Payment by credit or debit card is taken over the phone before the replacement volume ships.