Audi offers a TDI version of the TT, and Porsche is considering the idea of a four-cylinder Boxster. Now Mercedes-Benz has joined the club by reporting it’s preparing to offer a diesel engine option in the next-generation SLK.

The unit in question will be the same 2.2-liter “BlueEfficiency” 4-cylinder twin-turbo diesel currently offered in the C250 sedan, where it returns a claimed 54.3 mpg while spewing out just 138g/km of carbon dioxide. Although to previous generations the idea of a diesel convertible remains an anathema, the advance of particulate filter and common rail injnection technologies now common among the most advanced diesel engines make them a viable, earth-friendly option for open-air motoring.