The objective of maximum economic yield in fisheries requires the use of bioeconomic models for the estimation of appropriate economic-based catch or effort targets. These in turn require detailed information on costs of fishing, and how these costs may change under different fleet size and effort conditions. Economic information is generally collected (if at all) on an annual basis. While some costs can be easily designated as fixed or variable, others, such as repairs and maintenance, have both a fixed and variable component that is not identifiable from annual information. In this note, we present a means for separating these costs into a fixed and variable component for Australian fisheries and find that the ratio varies considerably by fishing method and environment. © 2014, © 2014 Taylor & Francis.