Germany is the world's most energy efficient nation with strong codes on buildings while China is quickly stepping up its own efforts, an environmental group said Thursday.

The study of 16 major economies by the Washington-based American Council for an Energy-Efficient Economy ranked Mexico last and voiced concern about the pace of efforts by the United States and Australia.

The council gave Germany the top score as it credited Europe's largest economy for its mandatory codes on residential and commercial buildings as it works to meet a goal of reducing energy consumption by 20 percent by 2020 from 2008 levels.

"We are pleased to win a second title in a week's time," Philipp Ackermann, the deputy chief of mission at the German embassy in Washington, told a conference call, alluding to his country's World Cup victory.

Echoing the views of the report's authors, Ackermann pointed out that Germany has achieved economic growth while improving efficiency and reducing harmful environmental effects of the energy trade.

"We all agree , I think -- the cheapest energy is the energy you don't have to produce in the first place," Ackermann said.

"Our long-term goal is to fully decouple economic growth from energy use," he said.

The study ranked Italy second, pointing to its efficiency in transportation, and ranked the European Union as a whole third. China and France were tied for fourth place, followed by Britain and Japan.

The report found that China used less energy per square foot than any other country, even if enforcement of building codes is not always rigorous.

"There's a lot more China can do, they do waste a lot of energy as well, but they really are making quite a bit of progress," said Steven Nadel, the council's executive director.

The study found a "clear backward trend" in Australia, where Prime Minister Tony Abbott is skeptical about the science on climate change. Earlier Thursday, Australia abolished a controversial carbon tax.

Australia was ranked 10th, with the council praising the country's efforts on building construction and manufacturing but placing it last on energy efficiency in transportation.

The study ranked the United States in 13th place, saying that the world's largest economy has made progress but on a national level still wastes a "tremendous" amount of energy.