In this work we employ the Neuro Fuzzy System hybrid algorithm to infer S ratio through the experimental magnetic susceptibility (χ) data measured in 90 samples, from a 670 meters thick sedimentary sequence, at the stratigraphic well Saltarin 1A (Colombia). The method is applied here as a means for pattern recognition of the major lithostratigraphic units encompassed by this well (i.e. Guayabo, Len and Cabonera Miocene Formations). The sets of fuzzy rules obtained work well only when used to infer S ratios within the same Formation from which they were derived. This is particularly noticeable in Guayabo, with lithological characteristics different to those of Len and Carbonera. The contrasts between these three Formations seem to be responsible for the inability of finding a unique set of fuzzy rules that could properly infer S ratio over the whole well using χ data only as the input variable.