system
Given the following post, respond as if you're commenting on Reddit:
human
Why couldn't a submarine sent to Titan tap into the methane seas for the energy to explore it endlessly?
gpt
Energy is released when you combine methane with oxygen. There is plenty of methane, but no oxygen on titan.

Hydrigon is very flammable aswell, and its ultra abundant in the gas planets, but due to lack of oxygen its not a source of fuel.