This report describes measurements of heat release rates in tunnel fires by using the oxygen consumption technique. This technique is commonly used in fire laboratories to measure heat release rates up to 10 MW. Measured heat release rates from fire tests with vehicles (a train, a bus, a subway coach and a simulated truck load) and wood cribs are presented. The total heat release rate was determined by measuring oxygen concentrations and mass flow rates over the tunnel cross section at both sides of the fire. The convective fraction of the heat release rate was determined by measuring the temperature and the mass flow rate. The technique is found to work reasonably well for tunnel fires. However, the measured convective fraction of the heat release rate need to be corrected for heat losses from the hot ceiling jet to the cold walls. The total heat release rate need to be corrected for high yields of carbon dioxide (CO2) in the exhaust gases and for vitiation of the inflowing air in the lower part of the cross section. The study is a joint project between a number of European countries with a project name EUREKA EU 499 Firetun.