Accurate predictions of the outcomes of droplet collisions (i.e. coalescence or bounce) are important for determining process performance. The outcomes of droplet collisions in gas-liquid systems have been well described in the literature, whereas studies focussing on droplet collisions in liquid-liquid systems are much less common despite their direct relevance to solvent extraction. The few studies that exist initiate droplet collision either via a jetting process whereby the two drops are ejected at high velocities from two needles pointing towards each other, or by bringing a droplet attached to needle slowly toward another droplet on a substrate. For the former configuration, it is very difficult to control where and how the drops collide, and introduces a significant amount of uncontrolled background flow in the continuous medium. In the latter configuration, the slow speeds are not representative of industrial conditions. We present experimental results of controlled droplet collisions in oil-water systems where the drop motion is driven by buoyancy. Two configurations are considered: a fixed collision where one drop is released from a needle and collides with another droplet pinned to a needle; and a free collision where both drops are released and collide with each other away from the presence of the needles. Numerical modelling is used to compare to experimental observations, using a sub-grid scale method to capture thin film drainage that is coupled to a volume-of-fluid method to capture droplet deformation. In direct contrast to liquid-air systems, we observe coalescence for off-centre collisions at low Weber numbers.