A three year old car that is low on oil? Why'd you need a quart? Burning or leaking? How long since your last oil change?
Bottom line:
If your low enough to matter, (just about) any oil is better than low oil. I know a guy who put Olive oil in his truck (it's all he had available) and drove it straight to the shop and had an oil change done.
If you think about how much a single quart of oil costs, you'll feel better about getting your oil changed before it gets low enough that you have to buy one (I'm guessing that the car has 4-5k miles on since the last oil change).
SAE is the Society of Automotive Engineers. They came up with a list of standards that must be met if you wanna call your oil SAE 10w30, SAE 10w40, etc...
If you look in your owners manual (RTFM), you'll see a section that suggests what oil to use based on what kind of climate you live in and what kind of driving you do. Most newer cars use 5W30 since it runs thinner and takes less energy to produce the required pressure (which increases economy). I think the Hybrid I use at work recommends 0W20.