Methylphenanthrene index

The methylphenanthrene index allows statements to be made about the maturity of petroleum . It is calculated using the formula

${\displaystyle MPI1=1,5*{\frac {(2MP+3MP)}{(P+1MP+9MP)}}}$

where X-MP stands for the methyl substitution on phenanthrene and P for the unsubstituted phenanthrene. The MPI 1 value increases until the end of the oil window and then decreases. The maximum value is at a vitrinite reflection of approx. 1.4. The isomers 1MP and 9MP are less stable in the lithosphere and are converted to 2 and 3 MP.