Private transfers with Ski Lifts is a great option too, as is hiring a car and driving
By bus:
Grenoble bus station is next to the SNCF train station and where buses from Grenoble Isère and Lyon St Exupéry airports also arrive.
Bus connections :
Transisère 3000: Daily service between Grenoble bus station and Rochetaillée (10 km from Oz Station), then take the free shuttle bus to Oz Station.You can also take Transisère 3000 to Rochetailée, then the Transisère 3010 to Allemont (7 km from Oz Station), then the free shuttle.