The Mini Cooper's mileage numbers have gotten a downgrade from the EPA.

Mini has become the latest in a line of automakers who have had to admit they were overstating their fuel economy numbers.

The British marque’s 2014 Mini Cooper actually gets anywhere from one to four miles per gallon less than originally claimed. The BMW subsidiary’s error follows in the tire tracks of Mercedes-Benz, Ford, Hyundai and Kia, all of which also have had to roll back their mileage claims.

Meanwhile, many consumers groups continue to complain that they’re routinely seeing real world numbers that lag what manufacturers post on their Monroney window stickers and use in their advertising. That’s leading to stricter enforcement and likely changes to testing procedures by the Environmental Protection Agency which oversees fuel economy regulations.

“Fuel economy values matter to consumers and automakers,” said Christopher Grundler, director of EPA’s Office of Transportation and Air Quality. “To provide consumers with the most accurate, reliable and repeatable fuel economy values, we are continuing to strengthen our oversight to ensure fair competition among automakers.”

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Ford was the first maker to get snagged by an audit of its mileage numbers and testing procedures, the biggest gap impacting models like its C-Max and Fusion hybrid models. Hyundai and sibling Kia were later caught up in a similar audit process. The Korean carmakers ultimately agreed to a significant payout to owners of the affected vehicles – such as the Kia Soul.

Earlier this month, Mercedes-Benz was found to have overstated the mileage of its C300 4Matic sedan by one mile per gallon in the City, Highway and Combined categories.

Mini’s recently updated 2014 Cooper and Cooper S models will now have to restate their mileage ratings, as well. The base 3-door with a manual transmission, for example, was originally rated at 30 City, 42 Highway and 34 Combined. That’s been revised to 29/40/33. The Cooper S 3-door with a manual sees its figures drop from 25/38/29 to just 24/34/28. Automatic transmission models lose one to three mpg.

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The Corporate Average Fuel Economy, or CAFE, and fuel economy ratings systems have come under repeated criticism over the past four decades. Consumers often complain they don’t get near the stated mileage.

Part of the problem is that fuel economy can vary widely, depending upon factors such as climate, altitude and driver behavior. But industry observers also fault EPA testing procedures – and the fact that manufacturers usually run their own tests for the under-staffed federal agency to then review.

In particular, the so-called Coast-Down test has come in for sharp criticism. It is intended to measure such key factors as a vehicle’s aerodynamics and the mileage-robbing friction within its drivetrain.

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The EPA has been increasing the number of audits it conducts since the Ford and Hyundai/Kia mileage gaps were uncovered. And, by year-end, it intends to revise key elements of its testing, according to Christopher Grundler, director of the agency’s Office of Transportation and Air Quality.

“Especially these days, when things are so competitive and customers are saying, ‘This is my No. 1 purchase criteria,’ it seems to me that [the EPA and the industry] both would want to have as much confidence as possible that the label value represents a good number,” he told trade publication Automotive News.

The EPA has revised its mileage testing procedures on a number of occasions over the years, most recently in 2008. That last effort was particularly focused on hybrid-electric vehicles, such as the Toyota Prius, which often had some of the biggest gaps between rated and real-world mileage numbers.