There are two commonly used correlations for determining the: viscosity of natural gases. These are the Carr, Kobayashi, and Burrows,(CKB) and the Lee, Gonzalez, and Eakin (LGE). The CKB applies to both sweet and sour gas, but the LGE was derived purely for: sweet gas. The CKB is a graphical correlation, and consists of two sets of graphs with. temperature as the correlating parameter (not easily adaptable for computer applications): On the other hand, the LGE is a set of :simple equations; and therefore can be easily programmed for a computer: The LGE is used in numerous computer programs, with no regard to the fact that it was not derived for sour gas. This study compares the LGE to the CKB graphs for both sweet and sour gases. A detailed comparison of the two methods using various gas mixture compositions, temperatures, and-pressures was conducted. The results illustrate that for sweet gases, the comparison is acceptable, and the LGE equation can be used for most reservoir engineering purposes. However, for sour gases, the differences between the LGE and CKB correlations can be significant. This leads to the conclusion that the LGE correlation; which was derived for sweet gases only; should not be indiscriminately applied to sour gases.