The purpose of this work is to suggest a steam-to-carbon ratio (SCR) control strategy for the start-up and operation of a fuel processor and to experimentally verify this strategy. To overcome ambient temperature variability and manufacturing deviations, a controlled SCR method (CSM) is suggested. The CSM controls the water flow rate independently through heat exchangers (HEXs) to maintain a constant inlet temperature of the reactors. To consistently satisfy the target SCR value, the remaining water after control is fed to the last HEX used as a buffer. To verify the CSM, seven gasoline fuel processors (GFPs) were constructed. The GFPs consisted of an autothermal reformer (ATR), hydrodesulphurization (HDS), a high-temperature shift reactor (HTS), a medium-temperature shift reactor (MTS), a preferential oxidation reactor (PROX), a HEX, and an exhaust gas burner. Water was individually supplied to HEX #1 similar to HEX #4 as a cool-side fluid. One of the GFPs was operated at a low (-32 degrees C) and a high (50 degrees C) temperature. The CSM maintained a constant inlet temperature of the reactors; only the inlet temperature of the PROX was affected by the ambient temperature thanks to the CSM. Temperature results for the other six GFPs showed that manufacturing deviations appeared only in the inlet temperature of the PROX by the CSM. To confirm the effect of the CSM on durability, 38 start-stop cycles were performed over 314 h of operation. The results showed that the repeated use of the CSM led to a slow degradation of efficiency, while the temperatures of the reformer and reactor remained steady during cycling testing. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.