What is the safest and most environmentally friendly way of disposing of vegetable oil?

mix the oil with about 4 times as much soil and compost it.

It’s fully biodegradable. You can dump it in a corner of your yard. Just wait until it;s cool.

Ooops @PerryDolia has a good suggestion, too.

Drink it.

I just dig a small hole in the garden, pour it in and cover it. If you are using a compost bin, it could get a little messy so then yep mix with soil first.

You can make lye soap with it instead. thus reusing it.

http://www.soapcalc.net/calc/soapcalcWP.asp

I thow it (and my used kitty litter) on the poison ivy in my fields. The ivy seems to be flourishing, living long and prospering.

can’t you use it as gas in some cars? like they have special engines in some cars that use used cooking oil for gas?