Stellar oxygen

Fusion shells in a mature massive star
wikimedia

"This diagram shows a simplified (not to scale) cross-section of a massive, evolved star (with a mass greater than eight times the Sun.)

Where the pressure and temperature permit, concentric shells of elements are burning inside the star

Hydrogen (H)
Helium (He)
Carbon (C)
Neon/Magnesium (Ne)
Oxygen (O) 
Silicon (Si) plasma

The resulting fusion by-products rain down upon the next lower layer, building up the shell below.

As a result of Silicon fusion, an inert core of Iron (Fe) plasma is steadily building up at the center.

Once this core reaches the Chandrasekhar mass, the iron can no longer sustain its own mass and it undergoes a collapse. This can result in a supernova explosion."
R. J. Hall
wikipedia 

And so these fundamentally important elements are blown sky high into the deep space and everything, including oxygen and also us, is made of this stellar stuff.