The first ads will start to appear in the shooter game Blaston, from Resolution Games, and in two other unnamed Oculus apps. Facebook say they won't use data stored on devices to target ads. However, a Facebook spokesperson says they will use data from your Facebook profile, as well as "whether you’ve viewed content, installed, activated, or subscribed to a Oculus app, added an app to your cart or wishlist, if you’ve initiated checkout or purchased an app on the Oculus platform, and lastly, whether you’ve viewed, hovered, saved, or clicked on an ad within a third-party app". In addition, Andrew 'Boz' Bosworth, Head of Facebook Reality Labs, tweeted that you'll be able to manage what ads you want to see and that "Ads in VR will be different from ads elsewhere and this is a space that will take time and people's feedback to get right". It does sound like Facebook is looking for feedback about these initial experiences and will expand later based on feedback. Link
Here's an advertisement within the Oculus Quest game Blaston:
