There are plenty of reasons to keep a bottle of olive oil in your pantry at all times. It's a super versatile oil, good for both cooking food and as an ingredient itself. (Olive oil pancakes, anyone?) There's even some compelling research out there that suggests eating olive oil is good for your health. But if you've got a who-knows-how-old bottle of olive oil sitting on your shelf, you might want to hold off before you drizzle it on everything. That's because olive oil can go bad, and it can happen more quickly than you think.
The folks at California Olive Ranch, which makes extra-virgin olive oil, explain the shelf life of olive oil is only 18 to 24 months after bottling. That window is seconded by the California Olive Oil Council, which recommends you use your bottle of extra-virgin olive oil within 12 and 18 months after the harvest date—and once that bottle's open, you really only have six months to use it all up before the quality dips. Another olive oil manufacturer Star Fine Foods have a slightly more liberal window, giving you six to nine months to use up an open bottle of olive oil. But you get the idea.
So how do you store olive oil to keep it as fresh as possible for as long as possible, and make the most of that six-to-nine-month window? Keep your bottle of olive oil away from direct light; this is part of the reason why stainless steel containers and green glass bottles are preferred for olive oil storage. And if your olive oil does come in a clear glass bottle, you might want to put it in a different container that doesn't let in as much light. (Our friends at Real Simple also recommend wrapping the glass bottle in aluminum foil if you don't have another container.) You also want to keep the olive oil at room temperature, if not slightly cooler than room temperature, and limit exposure to oxygen.
Before you go and get super strict about what olive oil you will and won't use, take come comfort in knowing that you'll know if your olive oil has gone truly rancid. The color will change, becoming darker, and it'll take on a nasty odor.
Really, the most surefire way to keep your olive oil fresh is only buy as much olive oil as you can reasonably use in about six months. But going through all that fresh olive oil shouldn't be a problem, since there are so many great ways to use it.