My fuel cap vented gasoline, violently. fuel ran down my body panels below the gas cap as vapor/liquid spewed out of the car. it seems the fuel system was over pressurized. i was at chinn's lake in colorado. elevation is roughly 11,000 feet. temp was around 70f. gas tank was around half full with premium gas from costco. from what i have read, it appears the gasoline began to boil and needed to vent. this can be from a faulty evap system, an overheated fuel system, ethanol in the gasoline, etc...