I have a quart (0.9 liter) of vegetable oil, and was wanting to get rid of it. I know you're not supposed to pour it down the drain, and was thinking that if I put it in the compost bin I would be feeding the worms and helping my garden. Are there any problems with that idea?
You can compost vegetable oil but when doing aerobic composting the disadvantage is that oil will reduce the amount of air that can get in your compost heap. If you add too much oil and/or don't aerate your heap properly the compost will start to smell and turn into an anaerobic process. Additionally oil may attract animals.
Recycling the oil via a local grease recycling program is the preferred option. If that's not possible you can compost it, but I recommend adding small amounts at a time.
Yes -- with caveats.
It will decompose. Even motor oil will decompose. (Don't use this as a way of disposing the used stuff. It has lots of ungood things besides oil by the time it's used.)
However it will attract animals, dogs, cats, squirrels, mice, rats, bears, porcupines,chickadees, bluejays...
A better solution: Mix it with oatmeal, or some other bird compatible cereal and put it out on your bird feeder.
You can also consider using vegetable oil as fuel for diesel vehicles modified for such purposes. There may be a site for people running on vegetable oil in your area, and you could donate your extra oil for this use.
You should also be aware that you can reuse cooking oil if you strain and refrigerate after cooking, and don't take it over 375 degrees F with food in it. You can watch for color changes or smells too, which indicate oil that should not be reused. More information on this can be found here: http://www.livestrong.com/article/532582-the-hazards-of-reusing-cooking-oil/