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...of course, being sealed in a plastic bottle will keep air and microbes from getting to the vegetable oil and it might last a really long time if you're lucky. But unless you sterilize everything and work very carefully to keep it that way, there's no way to be sure.
I recommend NOT using vegetable oil. It can spoil and turn rancid. We made an ant barrier for my mother's hummingbird feeder, and she filled it with olive oil the first time. Some few months later, ants invaded the feeder and investigation revealed that the oil went rancid, turning thick and gelationous... the ants could then walk right across it! After cleaning it up and refilling with mineral oil, it generally lasts at least a year before getting too full of miscellaneous debris and needing to be cleaned and refilled again, but the mineral oil remains liquid.