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Photographer: Krisztian Bocsi/Bloomberg Photographer: Krisztian Bocsi/Bloomberg

Mercedes-Benz topped a European lobbying group’s list of carmakers to overstate fuel economy for the second year in a row in an annual study that may receive extra scrutiny amid Volkswagen AG’s diesel-engine test scandal.

Vehicles built by Daimler AG’s Mercedes division used 48 percent more fuel on average than their published statistics claim, with gaps exceeding 50 percent on new A-, C- and E-Class models, Brussels-based Transport & Environment said Monday. BMW’s 5-Series and the Peugeot 308 produced differences between real-world and laboratory results of just under 50 percent. Across the industry, the gap widened to 40 percent last year from 8 percent in 2001, with the difference between published specifications and actual fuel use costing a typical driver an additional 450 euros ($500) yearly at the pump.

T&E based its figures on a 600,000-car analysis compiled by the nonprofit International Council on Clean Transportation. Another ICCT analysis, in 2013, prompted the U.S. probe that resulted in Volkswagen’s admission that it installed software to cheat on diesel emissions tests in some 11 million vehicles.

“Like the air-pollution tests, the European system of testing cars to measure fuel economy and carbon dioxide emissions is utterly discredited,” Greg Archer, clean-vehicles manager at T&E, said a statement accompanying the study. “The Volkswagen scandal was just the tip of the iceberg.”

Regulators’ Response

Following the Volkswagen scandal, the European Union is scrambling to assess weaknesses in a regulatory system that has laxer emissions tests than in the U.S. Environmental groups are pushing for tougher tests by 2017, while the United Nations is coordinating efforts for countries to harmonize automotive regulations, including environmental rules.

T&E’s report on Monday focused on fuel consumption and the carbon dioxide emissions it implies. That’s a different type of emissions than the nitrogen oxides, or NOx, that Volkswagen admitted to falsifying. Carbon dioxide is linked most strongly to global warming and not harmful for individuals, while other auto pollutants, such as NOx and fine particulates, can lead to respiratory diseases.

Other vehicles consuming close to 40 percent more fuel than official results included the VW Golf and Renault SA’s Megane, the T&E report said.

Daimler said that, as T&E doesn’t publish test conditions, “it’s not possible to properly examine” the results.

Worldwide Procedure

“Mercedes-Benz strongly supports the introduction of the so-called worldwide

harmonized light-vehicles test procedure, so that test results from the lab and real road driving are closer together,” said Matthias Brock, a spokesman at Stuttgart, Germany-based Daimler.

PSA Peugeot Citroen supports the more stringent test results coming into effect in 2017, said Pierre-Olivier Salmon, a spokesman. The Paris-based carmaker posted some of the best results in an ICCT ranking of the divergence between on-road tests and official fuel consumption, he said.

“It’s not news that there are differences between lab tests and real-world results,” said Michael Rebstock, a spokesman for BMW AG. The Munich-based manufacturer “is adhering to the rules and regulations. We also support efforts to reform regulation in the EU designed to bring results closer in line with real-world driving conditions.”

— With assistance by Jonathan Stearns, and Elisabeth Behrmann