Abstract: Water contains a certain amount of oxygen dissolved in it and the relative measure of this oxygen is called as Dissolved Oxygen (DO). The dissolved oxygen content in water can be increased by the process of aeration. The efficiency of oxygen transfer depends on many factors including bubble dimension, flow rate and nozzle diameter. Surface and subsurface aerations are two types of aerations. In the former, aeration is done by exposing water in the form of droplets or thin sheets to air and in the latter air in the form of small bubbles is allowed to rise through water. The objective of this study is to study subsurface aeration and the effect of variation in bubble size, superficial velocity, flow rate and nozzle diameter on the dissolved oxygen content in the sample of water taken. This is done by precipitating a small amount of salt in water by dissolving oxygen and measuring the amount of salt in the water before and after aeration. The bubble dimensions are calculated using image processing techniques. The results show that bubbles of smaller size with maximized surface area, take more time to reach the surface, increasing the residence time of each bubble in the water, allowing a better oxygen transfer rate.