Hi,
I'm brand new around here but I feel your pain. I run the blending/receiving area for a chemical manufacturer and we receive, store,blend and transfer quite a number of different fluids, mainly oils.
We use a few flow meters for estimates but thats about it. Obviously temperature is going to affect your readings unless that is accounted for. The meters we use can be calibrated, but if we send a different product through one then all bets are off.
Peristaltic pumps would be an option but it sounds like your flow is getting up there for that. In my opinion, any method that relies on measuring volume is prone to variations. We now do all our batch blending by mass on load cells. A pound is a pound no matter what the temperature is. I don't know if your process requires that level of accuracy but in my opinion, you can't beat load cells.
To tell the truth though, due to price, I arrived here looking into methods to determine fluid levels in storage tanks using ultrasonic range finding. I'll not get off into that now though. I can't say what the cost of a "legal for trade" flow meter for your process is but we have about 20 scales that are ISO certified and good to go and the cost isn't too bad... as long as people don't tear up your scales.
Measuring both volume and mass have their pros and cons so I guess it depends on your requirements...measuring from/to single vessel or multiple? Stationary or portable? Dedicated product or diverse? Level of required accuracy? Constant flow or start and stop?
You did ask for volume and if I'm preaching to the choir, we'll blame it on me being new here but I just want to remind you that the coefficient of thermal expansion can pose a problem for some processes.