Bigger is better right? More bang for your buck? Only if you don't mind rancid olive oil.
I, Erin, used to buy EVOO by the gallon (for cooking -- more on that in a minute), and even though I use olive oil* at a very rapid clip, by the time I'd get closer to the bottom of the container, the oil would always be rancid (that is, oxidized, smelling of crayons and old nuts, and no longer suitable for consumption. Ick!).
This rancidity is because you've got a few things working against you.
First: time. Time is not olive oil's friend. And it will inevitably take you more time to finish a gallon container than something smaller. The more time the container is open, the more time the oil is exposed to air, and the more it oxidizes and goes rancid.
The other issue with these large jugs is that, as you use more olive oil, that big bottle fills up with more and more air....which is just more and more air that will oxidize your oil. Time, together with lots of oxygen, will accelerate oxidation.
The third possible problem is the olive oil's quality. Olive oil sold in large containers *typically* isn't going to be of the highest quality because bulk olive oil just generally isn't meant for finishing, but rather cooking. As such, the oil will likely be lower in phenols -- that is, antioxidants -- and therefore will oxidize more rapidly than a higher-quality olive oil. To be clear, it's ok to cook with extra virgin that isn't the best of the best, but, scientifically speaking, it just may not have the same shelf life.
What's our recommendation? We believe in being very transparent about the fact that our oils are ideal for finishing, and we totally support using a lesser-quality extra virgin to supplement for cooking. If you go that route, and you don't run a restaurant and cook massive quantities of food, consider selecting a liter size from the grocery store of a brand that has a good reputation. Meanwhile, if you want to have more olive oil for cooking on hand, then just buy more liters so that your olive oil always stays fresh.
Finally, don't forget to store it in a cool, dark place, and use it within three to four months of opening, and, if unopened, within a year and a half of harvest. And, of course, use lots of PRMRY to finish your dishes!
*When I say olive oil, I'm always referring to extra virgin ;).