While prepping for the story I ran into a few facts that I found interesting.
The stabilized (*) HOCAN (High Oleic Canola Oil) in PET bottles was estimated to have a shelf life at ambient temperature of 6.8 years, while oil stored in LDPE bottles had an estimated shelf life of only 2.7 years. The estimated shelf life of HOSUN (High Oleic Sunflower Oil) at room temperature in PET is 2.6 years and in LDPE is 0.88 years. Source*1,000 ppm for ascorbyl palmitate, 200 ppm for tertiary butyl hydroquinone (TBHQ), and 200 ppm for mixed tocopherol
Using the same criteria, most vegetable oils have a shelf life of six months from date of manufacture.
Oxygen permeability rates (Oxygen. (g 25μ/m2/24h))
Low Density Polyethylene...8500
Polyvinylidene Dichloride film can be purchased on eBay if you want to use it to use it as an oxygen barrier between the LDPE cap of most bottles and the glass bottle. Saran Wrap in the US used to be polyvinylidene dicholoride but it is now polyethylene. Wrap sold under the brand name of Saran in Japan is still polyvinylidene dichloride.
Larger bottles have less surface area per unit volume so have better shelf life.
Lower temperature is favorable for longer shelf life.
Darkness is favorable for longer shelf life.
The largest, easy-to-acquire, brown glass bottles are the 40 ounce bottles that hold beer and malt liquor.
Oils that are low in the components that go rancid are Olive Oil, partially hydrogenated anything, peanut oil, tropical oils and some of the high oleic oils. The high oleic oils are currently expensive but production is ramping up as customers shy away from trans-fats.
The price spread between high oleic canola oil and "regular" vegetable oil is about $20 a gallon for HO canola and $8 a gallon for regular.
The fact that peanut oil is a very desirable oil for storage and only costs $11/gallon needs to be weighed against the possibility that one of your people might have a very severe, potentially fatal allergy to peanuts.
Your mileage may vary.