As long as you plan your dives and monitor your air supply, you should never run out of air. But in the event you or your buddy has an out-of-air emergency, there are several methods available for surfacing.

You can share your air supply with your buddy by allowing your buddy to breathe from your octopus or another alternate air source. If an alternate air source is not available, you can share a single 2nd stage by using a method called buddy breathing. Both of these procedures allow two divers to ascend together while sharing a single air supply.

If you find yourself out of air and your buddy is not immediately available, you'll have to exhale your last breath as you swim to the surface. You can make it to the surface by using the emergency swimming ascent or emergency buoyant ascent.

The pages that follow explain the process for each of these methods.