A key design aspect of room-and-pillar coal mines is the panel width (or number of entries in a panel), which affects unit mining costs and productivity. Traditional mine design approaches do not facilitate optimisation of unit mining costs and productivity as a function of the panel width. Discrete event simulation can be used to facilitate optimal panel width selection that minimises unit mining costs and maximises productivity. The objective of this study is to evaluate the impact of panel width on the cost and productivity of a room-and-pillar operation using discrete event simulation. The mining system is modelled as a discrete event model that estimates unit costs and productivity for a given panel width (number of entries). Data from a real-life mine is used to validate the model in Arena®. An optimal panel width is recommended based on simulation results.