An effective mechanical method of confining the oil spills in an open ocean is to use barriers such as floating booms. However, the confined oil may leak beneath a boom if either the towing speed of the boom or the amount of oil is too large. In this paper a simple mathematical model based on the potential theory is presented for the two-layer (oil and water) flow near a vertical barrier. A set of non-linear integral equations is formulated and solved numerically. For the indirect approach we adopted to solve the non-linear integral equations, the water velocity at the water–oil upstream contact point becomes a determining parameter of the final results. It is shown that the oil leakage under the barrier is impossible if the contact point is a stagnation one. For other non-stagnation cases, we were able to compute flows up to critical Froude numbers beyond which the oil will leak underneath the barrier.