ABSTRACT The analysis of vuggy and fractured reservoirs has been an area of significant interest in the past few past years. Several researchers have studied the characterization of these reservoirs and have looked for means of estimating values of the porosity exponent m for use in calculations of water saturation. We have found that some of the models for nonconnected vugs fail for certain combinations of matrix and non-connected vug porosities. The reason for the failures is an improper scaling of the matrix porosity. The same scaling problem is present in some of the models to analyze naturally fractured reservoirs but the magnitude of the error in the calculation of m is very small for most cases of practical importance. We present an improved model for reservoirs with non-connected vugs that is shown to hold for all combinations of matrix and non-connected vug porosities. The model is validated with data for carbonate reservoirs published previously in landmark works by Lucia (1983, 1995). We also present an improved model for reservoirs with natural fractures and/or connected vugs.