There has been a resurgence of interest in low-cost long-haul (LCLH) operations as airlines seek new growth opportunities. However, researchers have yet to evaluate and compare the relative efficiency of LCLH carriers in this competitive business environment. The purpose of this paper was to determine the relative efficiency of LCLH carriers in the Trans-Atlantic and Asia-Pacific markets. Data Envelopment Analysis (DEA) models were developed to compare the efficiency of five low-cost carriers: AirAsia X, Cebu Pacific, Norwegian Air, WestJet, current LCLH carriers, and JetBlue, a prospective LCLH carrier. The key findings from this DEA were that AirAsia X, Norwegian Air, and JetBlue were relatively efficient for all four quarters, whereas, Cebu Pacific was relatively efficient for three out of four quarters, while WestJet was relatively inefficient. Recommendations include suggestions for WestJet to lower its cost structure, and increase load factor, revenue passenger miles, and total revenue to achieve success with LCLH operations.