Ou 95 burns 1 quart every 700 miles, no leaks, lots of blue smoke. The jury seems to be out regarding additives or synthetic oil to slow down consumption. Any thoughts?

Synthetic is not a mechanic-in-a-can, and isn't likely to help.
Don't know of any additives which might solve this.
My guess, and it is only that, is that you probably have bad valve seals.

Were it mine, I'd probably get a treatment of Auto-Rx and try that. Relatively inexpensive, and has had some really good reports. At worst, it won't hurt anything and you'll be out a few bucks.

How many miles are on the motor, what WEIGHT oil do you use, and how religious have you been about oil changes? Additives won't help oil consumption and changing to synthetic oil in a worn motor will generally INCREASE oil consumption. You need to find out where the oil is going before you can stop it. "Lots of blue smoke" is a bad ($) sign.

-BTC

The car has 155,000 bought when it had 140,000 and then realised it was burning oil. we were told to use 10 w 30, but still no change in consumption. Will a compression test tell us anything?

A compression will tell you quite a bit and is a good starting point. If you have a gauge (they're not that expensive) it's an easy test to do on an 850 ( not easy on a sideways V6). It'll show you if you have a problem on one or all cylinders but it isn't specific. It will show loss of compression but won't tell you if it's a valve, piston ring or head gasket. As you're blowing blue smoke it's most likely piston ring or valve related. If you remove the spark plug(s) from a low reading cylinder(s) and shoot in a couple squirts of oil and retest, a rise in compression suggests a piston ring problem. Good luck!

bl

Using additives won't slow down that kind of consumption. How many miles are on the engine? Sounds like your rings are shot, valves are leaking, or head gasket issue near an oil port.

This car has 155,000 miles. We bought it with 140,000 and realized shortly after it was using oil.