Aviation accounts for about 3% of the current global energy consumption of 15 terawatts (TW). The global annual growth of energy use in the aviation sector is likely to be around 2.15% and will exceed that in other transportation sectors, although land transport will continue to consume the largest amounts of fuel. Figure 1 displays the historical improvements in energy efficiency in the aviation sector. Fuel use is determined by both operational and technological factors. The former includes the passenger load factor, ground efficiencies, taxi procedures, take-off and landing paths and circuitry (actual distance traveled versus a great-circle distance), and changes in the mixture of old and new aircraft and propulsion systems with time. Technology factors, focusing on materials issues, are described in greater detail herein.