A new report has been released by the International Council on Clean Transportation (ICCT) has ranked the efficiency of domestic operations by America's largest carriers, according to the Huffington Post.

Travelers have growing concerns about the carbon impact that results from travel, causing an interest in airlines that operate efficiently and have the fewest emissions. Three round trip, cross-country or trans-Atlantic flights cause as much pollution as the average American household produces each year.

Alaska Airlines was rated the highest. It uses fuel with 23 percent more efficiency than American airlines, which ranked among the least efficient.

Jet fuel is the greatest cost for airlines, so the efficient use of fuel determines how profitably the airline is operating.

However, ranking aside, the report showed all airlines aren't using fuel as efficiently as they can. Steps such as installing winglets, flying at more efficient speeds and towing jets on the ground would all contribute to more efficient use of fuel.

The report used fuel consumption data reported to the U.S. Bureau of Transportation Statistics using a new methodology that evaluates the efficient use of fuel based on two factors, which are access and mobility.

The efficiency of all airlines was compared based on size, network structure or type of service.

The focus on efficiency is only part of the environmental impact made by airlines. A study from Manchester Metropolitan University showed that a mandatory cap on airline pollution is the quickest and most effective tool to reduce pollution.

Because of this, United Airlines remains at the bottom of the list of airlines with a long-term environmental impact. The carrier has led lobbying action against mandatory caps and filed lawsuits to block action.  United wants the government to push the decision for a global cap to 2016.

United would actually be positioned to benefit from a cap because they are unlikely to hit it, allowing them to sell their excess pollution permits to other emitters.