Last week as I was running around in my daily driver, a 1994 Mercury Sable, I noticed a strong smell of gas coming in through the A/C vents, shortly thereafter, the car stalled. I was on my block thankfully, so it was no big deal. Opening the hood, it looked as if something had leaked into the engine compartment. The next morning, the car started up just fine and hasn't given me any problems until today when it did it again. It started with a barely perceptible vibration that I could feel in the pedal, followed by a strong gas odor and then the engine stalling. No signs of any new fluid in the engine compartment this time though. This time, I was able to piece together a few things about the situation. Both times it happened on a hot day, with the A/C running and after I had been driving around town for an hour or so. This time, I also noticed that there seemed to be a lot of pressure in the fuel system. When I loosened the gas cap, there was a very long and loud hiss of escapting gas vapors. It seemed once this pressure was relieved, the car was able to start up just fine and I drove home without incident. Looks like I'll be driving my nice car for a little while until I sort this out. Any ideas on what's wrong?