氧4分子（O₄），也被称作四聚氧。1924年，吉尔伯特·牛顿·路易斯首先预测了它的存在，以解释液氧不符合居里定律（顺磁性物质的磁化率与热力学温度成反比）的原因。现在看来路易斯的预测并不准确，但不是完全错误：计算机模拟表明，虽然液氧中没有稳定的O₄分子，O₂分子确实倾向于形成反平行自旋的双聚体O₄。1999年，科学家认为固态氧的ε相（压强大于10GPa下存在）中氧的存在形式为O₄。然而2006年时，X射线晶体学表明这种被称作ε氧或红氧的稳定相实际上是O₈。 然而，氧4作为一种存在时间很短的化学物质已经能用质谱法检测到。

The tetraoxygen molecule (O₄), also called oxozone, was first predicted in 1924 by Gilbert N. Lewis, who proposed it as an explanation for the failure of liquid oxygen to obey Curie's law. Today it seems Lewis was off, but not by much: computer simulations indicate that although there are no stable O₄ molecules in liquid oxygen, O₂ molecules do tend to associate in pairs with antiparallel spins, forming transient O₄ units. In 1999, researchers thought that solid oxygen existed in its ε-phase (at pressures above 10 GPa) as O₄. However, in 2006, it was shown by X-ray crystallography that this stable phase known as ε oxygen or red oxygen is in fact O
8. Nevertheless, tetraoxygen has been detected as a short-lived chemical species in mass spectrometry experiments.