1993 Ford Ranger loses all of its oil

I have a manual transmission, 4-cylinder, 1993 Ford Ranger pick-up with 132,000 miles. Every now and then (it's happened twice so far) as I am driving it will lose all of its oil in a matter of minutes. The oil gauge will drop to zero and the "check oil" light will come on. When this happens, I stop the truck and refill the oil (I keep a spare gallon in the truck). After refilling I can drive the truck again and it no longer loses oil. I have inspected under the engine after refilling and can see no leaks. Several weeks later at a seemingly random time, it will lose all of its oil again as I am driving. When it loses the oil, the engine compartment is dry, but the underside of the truck is covered in oil from it spraying around while driving. Again, I can not identify a specific source of the leak and cannot recreate the leak after refilling. Have you seen anything like this before.