It's down to engine condition, viscosity and oil volatility.

Engine condition - Leaks etc

Viscosity - Thicker oils are consumed at a lower rate generally

Volatility - The less volatile, better qualty oils will slow down consumption.

Fully synthetic oils (proper ones that is, not petroleum based) have lower evaporation rates at high temps because they are more thermally stable.

There is a standard test conducted which measures this for each oil. The oil is tested at 150degC and the %age of evaportaion is measured. Obviously the lower this figure the lower the consumption and the better the quality, the better the results are.

Cheers
Simon