Around $41bn of the estimated $90bn gaming market is spent on mobile and around $2.7bn on VR. A survey for game engine developer Unity Industries found that 62 per cent of gamers would regularly interact with ads for an in-game reward.
https://www.theregister.co.uk/2017/10/09/mobile_gaming_ads/
https://www.theregister.co.uk/2017/10/09/mobile_gaming_ads/