Changes

For these reasons, and also because of the possibility of fortuitous similarities between unrelated samples, gas chromatography seldom provides definitive positive correlations. It may, however, provide fairly definitive negative correlations. When used in conjunction with other correlation parameters, it can often be valuable for positive correlations as well, as demonstrated in the following two examples.

For these reasons, and also because of the possibility of fortuitous similarities between unrelated samples, gas chromatography seldom provides definitive positive correlations. It may, however, provide fairly definitive negative correlations. When used in conjunction with other correlation parameters, it can often be valuable for positive correlations as well, as demonstrated in the following two examples.

==Maturity difference example===

===Maturity difference example===

The figure below shows gas chromatograms of two oils from Wyoming. Both were sourced from the Permian Phosphoria Formation, but are reservoired in different fields. The bimodal distribution of ''n''-alkanes in the top oil is consistent with a lower level of maturity than that of the unimodal oil at the bottom. Comparison of these oils using gas chromatography for the purpose of oil–oil correlation must be done with caution because of the maturity differences.

The figure below shows gas chromatograms of two oils from Wyoming. Both were sourced from the Permian Phosphoria Formation, but are reservoired in different fields. The bimodal distribution of ''n''-alkanes in the top oil is consistent with a lower level of maturity than that of the unimodal oil at the bottom. Comparison of these oils using gas chromatography for the purpose of oil–oil correlation must be done with caution because of the maturity differences.