I actually just performed an oil change on my gf's daughter's 98 Corolla, which has the same engine your Prism has in it.
What shocked me was that when I did the oil change, I only got about 1 and 1/3 quarts of oil out of the motor. I double checked everything I did to make sure there wasn't more oil hidden somewhere, and then asked the daughter if she has had to add oil to the car. She had added a quart about 2 weeks prior to my oil change.
Next step was internet research.
That lead me to find out that these engines are "known" for burning oil at alarming rates, even early on in their lifespan. Some lucky people who were persistent with their dealers got their engines replaced under warranty. So I got the gf's daughter to promise to check the oil level every week or two, and let me know how much oil she needs to add to it.
Third and final step was to perform a compression test on the car.
I decided to mark the cylinders 1,2,3,4, from the passenger's side to the driver's side, as that's the way I look at the engine, while standing in front of it.
So my compression test gave me these numbers:
175, 155, 182, 176
Reran the test on the low cylinder, and it dropped down to 145.
Added oil to the cylinder, and it then jumped up to 235, and 230, on the next two tests.
Her can has 173k miles on it, and just came into her possession a couple of months ago.
I'm going to check the valve clearance the next time she comes back, which hopefully is in the next couple of weeks, and will try some decarboning chemicals, too. Maybe we will get lucky. If not, then we'll figure something else out.
But, if someone had asked me if Corolla's and Prisms had a history of burning oil before Saturday, I would have said no, and thought you were a crazy person.