Hey! I appreciate the feedback, but I think you have misunderstood the gameloop and upgrade system. Its probably my bad for explaining it poorly lol, let me try again:
Your O2 can be upgraded when you are outside the mine, using the ores you collect from the mine (the green stuff, but also different colors when deeper in the mine)
That, together with other upgrades make you able to get way further and eventually beat the game :)