I've heard of tanks rupturing and flaring up (not to be confused with exploding), but as far as I understand, explosions like in the movies just do not happen, or rather, are extremely rare and require the conditions to be perfect; i.e. an outside fire burns hot enough and long enough near a sealed fuel tank to cause a BLEVE. I don't know if there are relief valves to prevent this from occuring

I'm not an expert or anything, so take it with a grain of salt... or a handful <img src="/images/graemlins/grin.gif" alt="" />