Natural convection will occur in inclined cylinders if the interior fluid has density variations. For stably stratified fluids at large Rayleigh numbers, the flow will consist of thin boundary layers; the theoretical upper limit for the Nusselt number along a cylinder of any cross-sectional shape is shown to be: Nu = sin^-2ϑ when ϑ < O. (The angle from horizontal, ϑ , is defined to be negative when the heavy fluid is at the lower end.) Experimental data for heat and for salt convection in water show Nusselt numbers ranging from Nu = 1.5 at ϑ = − 36° to Nu = 10⁷ at ϑ = + 45°.