In the movies, it's apparently very easy for a car to blow up after being involved in an accident. In some genres, it's a surprise when this doesn't happen. However, in real life, very few car accidents cause the vehicles to catch on fire.
The National Fire Protection Association did a study in 2008 to see how common this was and if it was a legit safety concern for drivers all over America. What they found was that there were about 8,100 fires after accidents in a four-year span -- starting in 2002 and ending in 2005. This means there were over five post-accident fires each and every day.