Twenty-five of 30 vehicles tested on Australian roads failed to meet their laboratory test results, and 11 of the cars consumed 10 per cent or more fuel than expected.
The Australian Automobile Association revealed the findings in its latest round of on-road vehicle testing, which also found six models produced more noxious emissions than allowed in Australia.
The results come amid a greater focus on vehicle emissions, following the introduction of the New Vehicle Efficiency Standard in 2025 and after rising sales of hybrid cars.
The association tested a wide range of vehicles in the latest round of its $14 million Real-World Testing Program, ranging from large SUVs and vans to small cars, a ute and people-mover.
The vehicles are tested on a 93km route around Geelong in Victoria, with tailpipe emissions captured on urban streets, rural roads and motorways and compared to lab test results.
Surprisingly, a small SUV registered the greatest gap in fuel consumption during recent tests, with the Hyundai Kona Hybrid using 33 per cent more fuel on the road than in the lab.
Another small SUV, the Kia Stonic, used 26 per cent more fuel than expected, followed by the Hyundai i30 Hybrid (17 per cent), the Toyota Fortuner (16 per cent), and the Kia Sportage Hybrid (14 per cent).
Findings that one-third of the vehicles consumed more fuel on the road than in the lab indicated a widespread issue in the automotive industry, association managing director Michael Bradley said.
"It's becoming clear that carmakers continue to optimise their vehicles' performance for lab testing, meaning new cars are too often overstating their improvements in fuel use and environmental performance," he said.
"Some vehicles perform as advertised but most do not, and our program is seeking to reward carmakers that deliver genuine financial and environmental savings."
In addition to fuel consumption, six of the 30 vehicles tested produced more noxious emissions than allowed under the Australian standard, including the Ford Ranger ute, Toyota Hi-Ace, and Toyota Fortuner.
Five vehicles did buck the trend and use less fuel than expected, however, such as the Ford Transit van (nine per cent less), Lexus NX350h SUV (seven per cent less), and Mercedes-Benz GLC250 SUV (three per cent less).
The program, funded by the federal government, has examined emissions from 114 vehicles since 2023 and found 88 models failed to meet their promised fuel consumption.
The association will expand its tests to electric vehicles shortly, Mr Bradley said, and compare their on-road range to what consumers are promised.
"Range anxiety continues to be a significant barrier to EV uptake," he said.
