Have you been caught up in the minicar craze? These miniature vehicles are the darlings of the commuter world, offering excellent gas mileage and ease of parking in congested cities. You may not realize it, but there are at least 11 options if you are shopping for this type of vehicle. But here’s a cautionary note before you plunk down the money on minicar: you may be compromising safety under some circumstances in exchange for that excellent mileage.

The Insurance Institute for Highway Safety (IIHS) recently performed tests on 11 minicars, and only one (the Chevrolet Spark) won an overall “acceptable” rating in one critical test. In that test – the small overlap front crash test – part of the car’s front end hits a 5 foot rigid barrier at 40 miles an hour. This test is different from a head-on collision, because it involves only the small front corner of a vehicle, and the front wheel, suspension system bear the brunt of the crash. Serious leg and foot injuries can occur in this type of crash.

As a general rule, larger, heavier vehicles provide more protection than lighter vehicles, and minicars can weigh more than 1500 pounds less than the average model, according to preliminary federal data. “Small, lightweight vehicles have an inherent safety disadvantage,” Joe Nolan,IIHS senior vice president for vehicle research, said in a statement.”Unfortunately, as a group, minicars aren’t performing as well as other vehicle categories in the small overlap crash.”

So how did the minicars fare in the testing? Every minicar, including the Spark, received a “poor” or “marginal” rating for structural integrity, the most fundamental element of occupant protection, according to the IIHS. These are the two worst ratings possible. Four minicar models, including the 2014 Ford Fiesta, were rated “marginal”, and six models, including the Toyota Prius C, were rated “poor”. None of the models received the best possible rating of “good”. The Honda Fit and Fiat 500 were the worst performers.

Minicars are undoubtedly popular, and this genre of vehicle helps automakers meet consumer demand for more fuel-efficient vehicles as well as federal standards that call for a 50% improvement in vehicles by 2025. However, a prospective minicar purchaser should consider the likely use of the vehicle and the driving conditions and circumstances under which it will be operated, when considering whether a minicar is the right purchase.