Synthetic Oil, made for use in Polar/Tropical Regions!
My uncle owned a bulk Esso agency in Winnipeg back in the 70's and I worked weekends for him around the plant from the ages of 8 to 12. In the early 70's Esso released that oil and the stuff was unreal. Put it this way...if you didn't plug the block heater in at night, your vehicle simply wasn't going to start in the morning in the thick of winter because the oil would thicken so much that the engine wouldn't want to turn over.
When he poured that Mobil 1 into the 454 in his 75 Chevy crew cab, all he'd do is turn the key in -35 to -40 temps and that thing would fire right up. Never plugged his truck in again. It has its good points. lol