Groundwater contamination is a big challenge all over the world. Ex-situ remediation is general and most common remediation technique as far as groundwater remediation is concerned. Ex-situ remediation is a costly procedure and it can’t control the movement of contaminant plume in an aquifer. In recent decade, in-situ bioremediation has been proved to be cost effective and ecofriendly technology for remediation of groundwater. Organic contaminant e.g. gasoline compound, is remediated most effectively using this technique. In-situ bioremediation technique encourages growth and reproduction of indigenous microorganism, which enhances biodegradation of organic constituents in the subsurface. To inject oxygen and other nutrient at the contaminated plume, injection and extraction wells are used. In-situ bioremediation consist of a set of injection and extraction wells and it’s very important to decide optimal number of these wells to minimize the overall cost. Thus, simulation-optimization approach is important to decide variables concerned with in-situ bioremediation system. Simulation and optimization is a technique which increases the system efficiency. This paper will review various optimization techniques used for in-situ bioremediation and present a brief study on single and multi-objective optimization used for in-situ bioremediation system.