Our consumption is none. However, I would recommend carrying a full gallon (5 quart container even better) on board. I use to just carry just one quart to be able to top it off until I learned my lesson below.
Always make sure the dipstick is fully seated after checking the oil! I had even been warned both by Kenny and by posts on this site and tried to always double check but still I managed to not get it fully seated one time. I did not know it until the the boat automatically throttled back and sounded a low oil pressure alarm, had 4 quarts of oil in the bilge, a great big mess, and only one extra quart on board! The bad news in this situation is you don't get any alarm until you have lost 4 quarts! The good news is that the Volvo system cuts the throttle automatically when it senses a loss in oil pressure. I was able to flag down another boater who had a gallon of oil that he graciously gave me and wouldn't even let me pay for it. (Boaters are really nice people!). This is also where a 12V oil extraction pump comes in really handy as I was able to use my extraction pump to pump the oil out of the bilge once we got back to the marina. I pulled the fuse for the bilge pump and dumped 5 gallons of soapy (Dawn) water into the bilge and pumped it all back out with the extraction pump. Cleaned up the remaining splatter with paper towels and put the bilge pump fuse back in.
No problems since, runs like a dream, temp and oil pressure all good. Just triple check that dip stick!
I also can imagine that it would be possible to blow the oil out in other places (hoses, filter gasket, etc.) that it would make sense to have enough oil on board to get home.
Curt