I saw unexplainable lights in the same area & the same time frame that livestock was being mutilated.I was around 30 miles north of Green River driving a tanker truck on my way to a crude oil well to load when I noticed lights off to the West. At first I just thought they were from choppers in the area. There had been reports of livestock being mutilated in that area, so I figured they were ranchers checking out their stock. That is until they started moving vertically at a speed I knew wass impossible for a chopper to achieve. I pointed this out to my girlfriend, and she grabbed the flashlight and started flashing it in their direction. When one set of the lights went straight up and out of sight my girlfriens started hollering 'look baby, they're UFO's, at which time I freaked and grabbed for the light. In the time it took for me to grab the light away from her, one of the set of lights came to within a mile of us,(they were probably 20 miles away to begin with) hovered for a few seconds, took off to the West and was gone.