In a process and system for recovering sulfur from a process gas stream initially comprising a hydrogen sulfide containing gas and an oxygen containing gas, a control process and system respectively are provided. The sulfur recovery process includes a thermal step having a beginning followed by a catalytic step having an end. The control process includes first analyzing a composition of the process gas stream at a first location between the beginning of the thermal step and the end of the catalytic step, first controlling the oxygen containing gas having regard to that first composition, second analyzing the composition of the process gas stream at a second location downstream of the end of the catalytic step, and second controlling the oxygen containing gas having regard to that second composition. The sulfur recovery system and control system therefor are provided for performing the steps of the sulfur recovery process and control process respectively.