Not using all of an oak Barrel

Perhaps this has been asked before, but could not find an answer.

I live half a block down from a number of wineries in Missouri. They have used oak barrels for sale all the time. I want to use one for oak aged or for lambics and sours. However, I could never brew 55 gallons to put into the barrel.

My question is, can I put 10 gallons in the barrel and let set, or is that way too much head rooms in the barrel. Will I get too much oxidation, or will the co2 created by the beer create a barrier? Any help is appreciated. Thanks.

You can achieve some of the same flavors by using oak cubes in secondary....

Shoot you could buy the oak barrel then cut it into chunks and probably sell them here

It would be a problem, for the reasons your listed plus others

45gal of headspace is HUGE relative to the amt of beer in there, would you put a gallon of wort in a 6gal carboy?

Also, any areas of the barrel that are not in contact with liquid will dry out, could possibly then leak if moved and will allow in much more oxygen then it would otherwise

If you cant brew 55gal, see if you can talk some other homebrewers from a club in your area to join in, if not I would suggest just using carboys and if you want you can age in a small barrel ie 10gal for a couple weeks before you bottle

As far as i know a storage barrel needs to be full/for long storage it is topped up regularly
A barrel will never be completely airtight and will therefor not retain a protective layer of co2 as glass would