This entry was a little challenging to sort out, because the Swedish automaker Koenigsegg made two cars with similar specs and similar names, the CCR and the CCX, and top-10 lists elsewhere on the Internet refer to the models as if they were interchangeable.
For a while, the Koenigsegg CCR held the top slot with a reported top-speed of 250.7 miles per hour (403.5 kilometers per hour). Koenigsegg's Web site says the CCR took the Guinness record at the time, although, with just 14 CCRs produced, Guinness must have waived its requirement that 30 cars must have been built for a model to qualify as a production vehicle (or the requirement was instated later). In 2006, Koenigsegg phased out the CCR and brought in the CCX, which was designed specifically to meet United States safety and emissions standards. Like the CCR, Koenigsegg built just 14 CCXs over five years, so this car is super rare, and its eligibility for the Guinness record is questionable at best. And, like the CCR, its top speed is estimated at about 245 miles per hour (394.3 kilometers per hour). It might be easy to confuse the two cars, but sources agree that the record-setting run was made in 2005, which narrows it down.