Crude oil turns to gooey sludge when it gets cold. It isn't frozen per se, but it won't pump through a pipe either. When gasoline freezes it develops crystals in it that can clog any valve or filter. I got caught in a winter storm once where my car just died. I'd pull over to the side of the road and my car would start right back up. It took me an hour to go about 7 miles. the guy at the gas station told me the gas was freezing in the fuel line and when I stopped the engine heat would warm up the gas and I could go again until the crystals formed again. he sold me antifreeze for gas and it worked. I also had to put some cardboard in front of my radiator to block some of the cold air so our heater would work. This was years ago, so I don't know if this still happens in extreme cold.