Swiss Railways (SBB/CFF/FFS) operates a train from Geneva to Château-d'Oex hourly. Tickets cost $30 - $60 and the journey takes 53 min. MOB also services this route hourly.
How to get from Geneva to Château-d'Oex
From Geneve train to Montreux then line 120 train to Château-d'Oex. 2 h 25 min SFr 55. From Genève, Place de Neuve line 5 bus to Genève-Aéroport, train to Montreux, then line 120 train to Château-d'Oex. 3 h 40 min SFr 62. From Geneva drive to Château-d'Oex. 1 h 38 min SFr 22.