Formation flight has the potential to significantly reduce aircraft fuel consumption by allowing “follower” aircraft to fly in the aerodynamic wake of “leader” aircraft. However, this requirement for aircraft to be in close proximity for large parts of their journey raises questions about the suitability of flying in formation given the diverse range of existing flights and geographical regions. This paper demonstrates the potential for two-aircraft formation flight for three distinct case studies: long-haul airline, transatlantic airline, and low-cost airline, encompassing a range of typical airline regions and characteristics. The results indicate, even with only minor scheduling alterations, the potential fuel savings could result in saving hundreds of millions of dollars in fuel costs and reducing millions of tonnes of carbon dioxide emissions. An analytical geometric method for calculating all possible combinations of optimal routes is presented. This is coupled with a mixed integer linear program for providing an assignment of aircraft into formation pairs. A number of different key metrics, correlations, and predictive indicators help to determine which flights, airlines, and regions show “good” formation potential. Importantly, this paper also demonstrates these results for a wide range of drag-reduction possibilities and the impact this has on achievable fuel saving.