The heat release rate (HRR) of a fire in a tunnel is a crucial factor, both in terms of fire spread and smoke production. Key factors which influence the HRR are: 1) the nature of the burning item; 2) the tunnel geometry; and 3) the ventilation conditions. This article reports on work which has been undertaken over a number of years to model the dependente of HRR on these factors; the work is continuing. Specifically, Bayesian probabilistic models have been devised to model the dependence of the HRR of a fire on tunnel geometry and longitudinal forced ventilation and a deterministic model has been devised to model fire spread from one item to another in a tunnel similar to the Channel Tunnel; again with longitudinal ventilation. Key interim results are presented. © 2003, Baywood Publishing Co., Inc.