I like to chop a whole kilo of garlic at a time and then I add rice bran oil and store it in a jar. It has never gone off yet and because rice bran oil has no noticeable flavour it doesn't affect the taste. It also has a higher burn point than olive oil and it is a heart smart oil.
I recently found out that if you garlic is white it has been bleached, look for the purple stuff. Also we don't really know what the overseas garlic, another reason to buy local produce!