In Minecraft, the term "oxygen value" is not officially used. However, I believe you might be referring to the concept of air capacity or oxygen in water, which is relevant to certain gameplay mechanics.
Oxygen in Water: When exploring underwater in Minecraft, players need to manage their oxygen supply. This is indicated by the player's breathing animation and the air bubble indicator on the screen. Running out of oxygen underwater can result in drowning damage.
Air Supply:
Regaining Oxygen:
Nether Bricks: Some players refer to "oxygen" in terms of Nether Bricks. Nether bricks don't actually provide oxygen; however, they are often used to create underwater structures that prevent water from flowing into them. In this way, they retain air inside, creating a breathable space for players.
Enchanted Books and Tridents: Certain enchanted books and tridents (weapons) can have enchantments that increase underwater mobility. For example, the "Respiration" enchantment extends your air supply, and "Channeling" can occasionally strike a bolt of lightning, providing air.
Hunger and Oxygen: Oxygen management does not directly affect your hunger bar. However, you should still manage your hunger to maintain health and avoid taking damage.
In summary, while there isn't an explicit "oxygen value" in Minecraft, you do need to manage your air supply when exploring underwater to prevent drowning damage. This involves surfacing to breathe and considering the placement of Nether Bricks to create air pockets.