Saturn’s moon Titan is covered in lakes of methane. On Earth, there are massive deposits under oceans and kept solid by the delicate balance between pressure and temperature: much of it near the Arctic. I have seen a lot of stories about the water locked up in rocks deep in the Earth’s crust. I haven’t seen anything about the possibility of methane and CO2 dissolved in that water…but then, we already have enough to burn the planet.

https://www.theguardian.com/world/2021/jul/03/eye-of-fire-gas-leak-sparks-huge-blaze-on-ocean-surface-off-mexico

Fun times.