Two series of 16 and 18 laboratory fire experiments were conducted to explore the respective roles of radiation and convection heat transfer in slope effect on fire spread. The first series attempts to measure fuel temperature and gas temperature simultaneously and at the same location using an infrared camera and thermocouples respectively. The second series measures the incident radiant heat flux as would be received by a small fuel bed volume ahead of the fire line. These measurements are used to compute a fuel bed heat balance for each slope angle (0 degrees, 10 degrees, 20 degrees and 30 degrees). Overall, radiative heating is found to be the heat transfer mechanism that dominates in the slope effect between 0 degrees and 20 degrees, but close to the fire line (<10 cm), the flux due to convective heating is also significant, reaching one-third of the net heat flux at a 20 degrees slope angle. When the slope angle increases from 20 degrees to 30 degrees, the rate of spread rises by a factor of 2.5 due to a marked increase in convective heating, while radiative heating no longer increases. Far from the fire line, cooling by convection is found to be substantial except at the 30 degrees slope angle.