  Interlibrary loan (ILL) services are used to fill the gap between academic
libraries' collections and the information needs of their users. Today's trend
toward the cancellation of serials "Big Deals" has increased the importance of
clear information around ILL to support decision-making. In order to plan the
cancellation of a journal package, academic libraries need to be able to
forecast their total spendings on ILL, which requires to have an appropriate
estimate of what it costs to fulfill an individual ILL request. This paper aims
to help librarians answer this question by reviewing the most recent academic
literature related to these costs. There are several factors that may affect
the cost of an ILL service, including the cost of labour, the geographic
location of the library, the use of a ILL software, and membership to a library
consortium. We find that there is a wide range of estimates for ILL cost, from
$3.75 (USD) to $100.00 (USD). However, Jackson's (2004) figure of $17.50 (USD)
per transaction remains the guideline for most researchers and librarians.
