Koenigsegg Agera R: 260 miles per hour (418.4 kilometers per hour)
Yeah, the Swedes made the list again -- this time with the Koenigsegg Agera S. The Agera S is a more formidable competitor for a top-slot than the CCR. It boasts a "theoretical" top speed of 273 miles per hour (439.4 kilometers per hour) according to the manufacturer, but the best anyone's been able to do is about 260 miles per hour (418.4 kilometers per hour). It's equipped with a 5-liter, twin-turbo V-8, which yields a little less power than some of the competition, but the car's light weight makes up for a lot.
Koenigsegg has been chasing Guinness world records for a while, and achieved four between 2003 and 2011 [source: Spinelli]. The Agera R actually beat the Bugatti Veyron Super Sport in 2011, although not in the all-important "fastest car" category. Instead, the Agera R showed off its skills by accelerating from 0 to 300 kilometers per hour (186.4 miles per hour), and then braking back down to 0, in just 21.19 seconds. That beat the Veyron Super Sport's time of 25.3 seconds by a rather comfortable margin. Maybe the Koenigsegg Agera R isn't the fastest car in the world, but its drivers are probably pretty happy with its proven acceleration and braking prowess.