Crude oils have been analysed for isopropylmethylphenols using GC-FID,
GC-MS and GC-FTIR techniques. Six of the 10 isomeric isopropylmethylp
henols have been identified in crude oils by comparison of their chrom
atographic behaviour and infrared and mass spectral properties with au
thentic standards. The relative abundances of isomers vary among the s
amples, however three different types of isomer distribution patterns
have been recognized. The relative abundances of isomers in the first
type are at or near equilibrium values. In the second type, isomers wi
th isopropyl groups in the ortho and para positions are abundant and m
ay represent the products from isopropylation of cresols. A third type
of crude oils has high relative concentrations of the natural product
s carvacrol and thymol. Because these compounds occur widely in extant
conifers and angiosperms, their presence in crude oils whose source r
ocks were deposited when these plant types were widespread suggests th
at they also originate from these plants.