The long-promised diesel revolution that was supposed to hit U.S. shores five years ago is finally beginning to come to fruition, but we'd still hesitate to call it a full-fledged "revolution" just yet. Maybe "incremental advancement." On a model-by-model basis, more diesel models are being offered, prompted largely by tightening CAFE standards. One of the latest to add a diesel variant is the BMW X3. The X3 always seemed like a natural for the diesel treatment, and the diesel option certainly has improved fuel economy relative to its gasoline-powered stablemates but not quite to the dramatic level some might have expected. The officially announced ratings for the 2015 BMW X3 xDrive 28d are 27 city and 34 highway, for a significant combined rating of 30 mpg.

This compares to the 22/32 and 26 combined rating for the X3 28i model and to the 24/33 and 28 combined for its closest marketplace competitor, the Mercedes-Benz GLK250 Bluetec. Gasoline direct-injected turbo engines employ many diesel-like technologies that have helped them narrow the efficiency gap with diesels, accounting for the small 2 mpg highway difference. The 5 mpg city fuel economy edge of the 28d is significant and helped give the diesel its 4 mpg combined edge over the gas model.

However, in our experience, diesel vehicles can sometimes exceed their EPA estimates, so the real-world difference between the 28i and 28d could be even greater. Expect even more diesel models to come on the market in the next two to three years as the tougher CAFE standards loom on the horizon.

Source: EPA