According to thefreedictionary, "transferrer" is someone who transfers something. However, it also lists the alternate spelling "transferer", with only one r in the middle. For the related "transferred", it does not list a variant with only one r.
So, which one is correct? Is there a geographical preference to using one or the other?
This reminds me of a famous misspelling in the specification for the HTTP protocol used by the internet, "referer", which as generally established should have been spelled "referrer". Now as "referrer" relates to the verb "to refer" and "referral", and there is "transferral", it seems logical to me that "transferrer" is spelled with two r as well. However, thefreedictionary again also lists "transferer".
Note that I am not asking about why the consonant is doubled, but which of both variants that seem to be common is the correct one.