I read in alot of your posts about looking at this, I have no idea what it is and what relevance it has on a bottle of wine. Can anyone help clarify this for me?

google ullage for a complete answer. But in essence, fill levels hint at the storage conditions the bottle has gone through.

This refers to the amount of space between the bottom of the cork and the top of the wine when the bottle is standing upright. New bottles that are properly filled should have about 1/4" of air between the wine and the cork. Over time, some wine may be lost due to evaporation of leakage. A small loss is nothing to worry about, especially in older bottles, but when the air space gets large and the level of the wine drops below the neck of the bottle, it might indicate a problem. So, the fill level is a measure of the condition of a particular bottle and a possible indication of the condition of the wine in it.

Thanks Doug and WEc, my next question is, if the wine is below the neck of the bottle do you still take a chance on the wine? Or if you buy a bottle online and it comes to you this way, what do you do? This is sort of a different topic, but if the cork is pushing upwards through the foil, how much is too much?

I'd pass on a wine with that much ullage (space between the cork and the wine), unless the seller offered me a guarantee that I could return the opened bottle for a full refund if it turned out to be bad -- which it more than likely would.

If someone sold me a bottle without disclosing such a defect, I'd try to get my money back and I'd flame the bastard if he refused, maybe even sue if it was valuable enough.

As for the pushed-up cork, if it's above the top of the bottle by more than a tiny bit, it's an indication that the bottle may have been exposed to heat or possibly extreme cold (water expands when it freezes). Either way, the wine would undoubtedly be severely damaged. Reject any such bottle, too.

I don't have experience buying online as I don't have exposure to this avenue. My general impression would be similar to the advice above. I wouldn't chance a wine with a low fill. As for the cork, it should be flush.

A tidbit of interest along this same line is the issue of topping up bottles. Some makers, especially ones of high end wines, will sometimes agree to inspect, open, then "top off" old bottles that have lost some of their wine over time. Penfolds has made it a duty to do this for owners of their premium Grange Shiraz blend. I don't know about other makers' practices, but in the Grange case, the wines, after being opened and judged to be in good quality, are topped off with a small amount of a more recent vintage.