Buried pipelines are subjected to fluid pressure (oil/gas/water), axial loads, moments, and complex load combination histories. As a result, they may develop large compressive strains and curvatures leading to formation of localized buckles or wrinkles in the pipe shell. Recently, full-scale tests on 12.75″ diameter (NPS12) energy pipes have been carried out at the University of Alberta to study the behavior of wrinkle development and the ultimate limiting strains at the wrinkle locations. Different internal pressures, and axial loads were applied to produce a wrinkle, followed by load variations intended to produce fracture that could develop in buried pipelines in the field. Three different axially loaded tests are reported. Two different internal pressures were applied, namely, (i) 0.8py and (ii) 0.4py, where py is the required internal pressure to cause the yield stress of the pipe material to be developed in the circumferential direction. Also, two different specimen lengths were adopted. They are: (i) 406 mm (16 inch) and (ii) 736 mm (29 inch). All specimens were loaded axially until the wrinkle formed. It was observed that the pipes are highly ductile and very large compressive strains can be developed without fracture or leakage in the pipe wall. Because the pipe specimens of the first two tests did not fail (i.e. fracture) under monotonically increasing displacements and strains, the third wrinkled specimen was subjected to load histories involving strain reversals. This load history resulted in a low cycle failure after a very few cycles. The paper addresses test procedures, buckling and post-buckling behavior of NPS12 energy pipelines and relates them to three different types of strain measures, namely, material strain, wrinkle strain and overall strain as observed from these tests.