Check the Owners Manual and look on the container for the Specifications that the oil meets. Take a look at PQIA.org for a more detailed explanation. Ironically, simply go to your local Toyota dealership’s parts department and ask for the oil and filter for your particular car. That’s the simplest way.
I don't habe the Prius but my car has the same 1.8L 2zr-fxe engine and my owners manual specifically states 5w-30 is fine. I didn't notice any mpg drop when I went from 0w-16 to 0w-30 although I am sure there was a drop.
