The paper investigates buckle propagation in deep sub-sea pipelines. Experimental results are presented using ring squash tests and hyperbaric chamber tests, and are compared with a modified analytical solution and with numerical results using finite element analysis. The experimental investigation was conducted using commercial aluminium pipes with diameter-to-thickness (D/t) ratio in the range 20-48. In contrast to conventional cylindrical pipe, a faceted cylindrical geometry is also investigated. Preliminary analysis of a faceted pipe shows that a substantial increase in buckling capacity can be achieved for the same D/t ratio.