Don't know if you chaps realise it but all oil will 'boil off' to some degree, not exactly but its the easiest way to discribe it. Cheaper oils will be more volatile than the high spec ones. It would not be uncommon for a 10-15% + loss to occur! The way to find out what your oils volatility is will be to look at its spec sheet; Noack Volatility is what you are looking for and you need the lowest you can find in whatever your choices of oil are. If the brand concerned doesn't publish such figures then don't buy it! I know that Amsoils figures are generally 5-7 dependant upon the oil, (I also know that these are some of the lowest figures you will find) but check the figures for your oil, if they are 9-10+ (quite likely) you will loose 1/2 as much again never mind the burning of the oil!
The next general rule is that if you have a car that is burning more oil that you think is acceptable you can reduce this by stepping up one thickness of oil, (ie it becomes harder to get past the rings and valve guides) Try a 5w-40 perhaps. What you want to steer clear of is a 0w-40 as this is often a weak oil that literally gets its viscosity improvers chopped up by the piston rings and so becomes thin and therefore burns.
Hope all this makes sense, try a low volitility oil for starters, as theres a lot more to good oil than most people think.