We report multifractal f (α) spectra obtained from petrophysical well log data from a large scale oil reservoir. The present analysis foes far beyond previous analyses based upon a single scaling exponent such as the Hurst exponent or the exponent obtained from Fourier analysis. Some of the data indicate an underlying return map. Return maps (deterministic dynamics) generate f(α) spectra. In addition, we report that the Hurst exponent is not uniquely defined for deterministic chaotic maps where initial data are chosen that produce statistical independence in the distribution of iterates.