Δ18O
= Δ18O
{wiki=Δ18O}
Δ¹⁸O (Delta oxygen-18) is a measure of the ratio of stable isotopes of oxygen, specifically the ratio of oxygen-18 (¹⁸O) to oxygen-16 (¹⁶O). It is expressed as a difference in parts per thousand (‰) compared to a standard reference material, typically Vienna Standard Mean Ocean Water (VSMOW).