Crude oil spectral signatures and empirical models to derive API gravity

•A spectral library with 37 types of crude oils (light to heavy) was produced.•Oil samples were spectrally characterized in the 350–15,000 nm interval.•Crude with different °APIs show particular infrared absorption features and metrics.•Multivariate predictive models based on oil spectra proved valid in estimating °API.•Oil spectra can be used to map crudes exposed at surface using remote sensing.