A process for the preparation of sulfuric acid comprising: burning a source of sulfur in a gas comprising excess oxygen to produce a sulfur oxide-bearing gas stream comprising a combustion gas comprising sulfur dioxide and oxygen; contacting the sulfur oxide-bearing gas stream comprising said combustion gas with a catalyst for conversion of sulfur dioxide to sulfur trioxide, thereby converting the sulfur oxide-bearing gas stream to a conversion gas containing SO 3; contacting the conversion gas in a primary heat recovery absorption zone with a primary absorption liquid comprising sulfuric acid, thereby transferring sulfuric acid from the conversion gas to the primary absorption liquid; introducing water vapor into the sulfur oxide-bearing gas upstream of the primary heat recovery absorption zone with respect to the gas flow direction in a proportion sufficient to increase the equivalent water vapor content to at least 0.40 moles per mole total equivalent sulfur oxide gas content in the gas entering the primary heat recovery absorption zone; circulating said primary absorption liquid between said primary heat recovery_absorption zone and an indirect heat exchanger in which heat generated by reaction of sulfur trioxide and water, condensation of sulfuric acid, and/or absorption of sulfur trioxide into the primary absorption liquid is transferred to a heat transfer fluid, thereby heating the heat transfer fluid to at least 150°C; contacting the gas stream exiting the primary heat recovery absorption zone with a secondary absorption liquid comprising sulfuric acid in a secondary absorption zone, residual SO 3 contained in the gas stream entering said secondary absorption zone being recovered as sulfuric acid in the secondary absorption liquid; controlling the rate of delivery of secondary absorption acid to the secondary absorption zone to maintain the difference between the local bulk temperature of the gas phase and the local bulk temperature of the secondary absorption liquid phase with which the gas is in contact not greater than 25°C at both the liquid inlet and liquid exit of the secondary absorption zone; and controlling the concentration of the secondary absorption acid entering the secondary absorption zone to provide a net available water supply to the secondary zone sufficient to assure that the composition of the gas exiting the secondary absorption zone is equal to or above the azeotrope composition with respect to water content and equal to or below the azeotrope composition with respect to SO 3 content. burning a source of sulfur in a gas comprising excess oxygen to produce a sulfur oxide-bearing gas stream comprising a combustion gas comprising sulfur dioxide and oxygen; contacting the sulfur oxide-bearing gas stream comprising said combustion gas with a catalyst for conversion of sulfur dioxide to sulfur trioxide, thereby converting the sulfur oxide-bearing gas stream to a conversion gas containing SO 3; contacting the conversion gas in a primary heat recovery absorption zone with a primary absorption liquid comprising sulfuric acid, thereby transferring sulfuric acid from the conversion gas to the primary absorption liquid; introducing water vapor into the sulfur oxide-bearing gas upstream of the primary heat recovery absorption zone with respect to the gas flow direction in a proportion sufficient to increase the equivalent water vapor content to at least 0.40 moles per mole total equivalent sulfur oxide gas content in the gas entering the primary heat recovery absorption zone; circulating said primary absorption liquid between said primary heat recovery_absorption zone and an indirect heat exchanger in which heat generated by reaction of sulfur trioxide and water, condensation of sulfuric acid, and/or absorption of sulfur trioxide into the primary absorption liquid is transferred to a heat transfer fluid, thereby heating the heat transfer fluid to at least 150°C; contacting the gas stream exiting the primary heat recovery absorption zone with a secondary absorption liquid comprising sulfuric acid in a secondary absorption zone, residual SO 3 contained in the gas stream entering said secondary absorption zone being recovered as sulfuric acid in the secondary absorption liquid; controlling the rate of delivery of secondary absorption acid to the secondary absorption zone to maintain the difference between the local bulk temperature of the gas phase and the local bulk temperature of the secondary absorption liquid phase with which the gas is in contact not greater than 25°C at both the liquid inlet and liquid exit of the secondary absorption zone; and controlling the concentration of the secondary absorption acid entering the secondary absorption zone to provide a net available water supply to the secondary zone sufficient to assure that the composition of the gas exiting the secondary absorption zone is equal to or above the azeotrope composition with respect to water content and equal to or below the azeotrope composition with respect to SO 3 content.