Quite a while ago we discussed this word quite extensively. I'm still disgusted with OED
talking about "negative ullage". But here's a new use of it, by NASA. You might want to
read whole episode in Engines of Our Ingenuity 934.

"That means containers need complex baffles that let
surface tension position the liquids. NASA uses the
old English word ullage to describe that process.
Ullage once meant the empty space in a barrel of
wine. Now we use it for the empty space in a barrel
of liquid oxygen. "