Batch Searching in OCLC
General process

In the Connexion client, under the Batch menu, select Enter Bibliographic Search Keys.
Select Import, and select the text file you’d like to import. A prompt will ask if you want to delete the original import file. Make sure to select No.
Make sure you save the batch.
Under the Batch menu, select Process Batch.
Select the file containing the search keys you entered by clicking the box next to it. If you save the search keys to your default save file, you will see a red check mark. You do not need to select an authority file. Select Online Searches in the Process box. Click OK.
When the search is complete, a Batch Search Report will display. You will need to manually search for any titles that come up as errors. This report will also show you if more than one record matched any of your searches. It may be helpful to print this report if you have a lot of errors or searches with multiple matches.
When you open your save file again, these records will be there.
If you want to export a batch of records from OCLC to MARCEdit, you must go into Tools →Options, and change the Destination to File:(Prompt for file name). Then click Edit to name the file and location. Don’t forget to change it back after the files have been exported.

OCLC numbers (the easiest way to batch search)

If the vendor provides a list of ISBNs in a spreadsheet, you will need to put them in a text file. You can just highlight the column and copy and past into Notepad.
Save the file. I usually name it vendordate, in case I need to find it later.
You will either need to select OCLC number as the default index or insert an asterisk before each number.

ISBNs

Searching by ISBNs will often retrieve many, many hits, and have at least a few errors. This is because eISBNs appear on records for print editions. Several records may also exist for the electronic version, including records cataloged in a language other than English. You will probably want to limit the search to records cataloged in English.
If you have a spreadsheet with the ISBNs, insert a column before the ISBN column. Fill in this column with ll: (that’s two lowercase Ls). Copy these two columns together, and paste them into Notepad.
In Notepad, you may need to remove any space between the colon and the ISBN, using Find and Replace. You can copy the space between the two, paste the space into the “Find what” and leave the “Replace with” blank. Then click Replace All. This should delete all the spaces.
Save the file. I usually name it vendordate, in case I need to find it later.