There is such thing: "I use Mobil 1, 0W-40 as it’s better then 0W-20 which is water and that 0W-40 is the only true synthetic oil made by Mobil." - orenji Is Mobile 1 High Mileage oil a bad match for the Prius? | PriusChat
But it's not legit per SAE standard which defines viscosity grades. Any claimed grade not in the standard is just marketing BS.