Produced fluids from SAGD process usually includes sulfides, either naturally occurring or generated from an aqua thermolysis process within the active chamber in the reservoir. The sulfide, is dealt with in different ways depending on the concentration and whether found in the water, bitumen or gas. Hydrogen peroxide has been successfully used to eliminate sulfides from the produced water phase in commercial SAGD operations in Alberta for over a decade. It has been proven effective in oxidizing sulfide to avoid H2S generation in downstream processes. An additional benefit is a less corrosive produced water, and oxidation of other organic sulfur species. It has been postulated that peroxide could be injected further upstream in the SAGD process. This could decrease or eliminate sulfides in more of the process. This could decrease the need and/or cost of downstream H2S mitigation steps. This application has been simulated in the laboratory at higher temperatures and increased content of hydrocarbons imitating the upstream process. Under these conditions, the reaction between hydrogen peroxide and sulfide is preferential and fast.