Volume: 27 • Number: 3 • Pages: 451-462

We use convex optimization to provide a rigorous proof of de Finetti’s retention result for proportional reinsurance. We then extend this result to variable quota share reinsurance and surplus reinsurance with table of lines. We demonstrate by a numerical example that in general neither variable quota share reinsurance nor surplus reinsurance with table of lines may be considered as optimal reinsurance structures.