Continental Airlines has made efforts to minimize the negative environmental effects of commercial aviation. For example, the carrier invested over $12 billion for the purchase of the current 270 fuel-efficient aircraft and related equipment that make up part of the airline's fleet. These efforts have contributed to significant reductions of greenhouse gas and noise emissions, and have decreased fuel consumption by 45% per mainline revenue passenger mile over the past decade. Continental Airlines was also one of the first carriers in the world to fit winglets to as much of its fleet as it could, reducing fuel burn by 3–5%.