How to know if my car will make a 300 mile round trip?

In response to that above answer... "not worrying about it" will get you stranded on the side of a highway. 300 miles isn't that far, so don't worry TOO much, but don't be ignorant.. that's just stupid. Try to find the nature of this oil leak if it's not too trivial, and always make sure the oil is topped off. Low oil pressure will ruin an engine in a matter of minutes. As was stated above, check belts, pulleys, fluids. Pay attention to the serpentine belt and those pulleys, they are common fail items. If any pulley makes any noise when spun, it may be nearing the end of it's life. Likewise, if the belt itself is dry and cracked, it may soon break. Make sure there's enough coolant, the oil is good, etc. Have spare oil if your leak isn't rectified, get AAA, pop in a good CD and enjoy the drive.