How long does conventional engine oil last?

TO BE SAFE I CHANGE MINE ONCE A YEAR THATS WITH HEAVY EVERYDAY DRIVING,IF NOT THEN IN 2 YRS,ALSO DEPENDS ON OIL QUALITY,SOME BRANDS GIVE A LONGER LIFE,BUT STILL 1 A YEAR & MY ENGINE STAYS PRETTY CLEAN & RUNNING SMOOTH...I USE ROYAL PURPLE ENGINE OIL & ROYAL PURPLE TRANNY FLUID & R.P REAR END GEAR OIL....FOR ME & CAR BOTH ARE HAPPY..