Loot stolen from Mills and Markets are around 15%, and each age has a maximum cap, 450k in global. 10% can be nicked from the CP. So if you have more than 3m in mill/markets it's better to withdraw it into mills/markets or the max loot available is 450k + 200k (if you have 2m in the CP) = 650k. All in the mills/markets keeps the cap at 450k.
Oil is 4% wth a 4k cap, so once you're over 100k oil, don't keep the excess in the CP.