A new modification is developed on conventional Claus process to increase the overall sulfur recovery as well as to decrease the costs. The modification combines both oxygen enrichment and recycling. The process is simulated and studied for various N-2/O-2 ratios with and without using SURE double combustion technique. The predictions show that using pure oxygen in combustion, condensing water vapor in a condenser following the first sulfur condenser and recycling the effluent gas to combine it with fresh acid gas feed leads to large savings in the production cost and to a clean environment. However, it leads to a high adiabatic flame temperature which exceeds the maximum allowable temperature of the furnace material of construction as well as its refractory. To avoid these effects, it is necessary to use SURE double combustion technique. The oxygen flow rate to the first combustion stage should not exceed 78% O-2. (C) 2004 Elsevier B.V. All rights reserved.