The sealing mechanism of API round thread includes the use of thread compound which is used to seal leak passages. These leak passages are helical capillaries found at the roots and crests of the thread tooth and vary in area according to the size of the thread tooth as well as thread tolerances. The thread compound viscosity is a critical parameter to achieve maximum sealability. This study measured the viscosity of thread compound under various temperatures. It was found that viscosity of thread compound falls in the range of 285,667 cP and 47,758 cP when measured between 32.9 0F and 121.5 0F. This information is very important because thread compound is essential to the function of open thread connections. The investigations were focused on API Modified Compound since it is widely used in the industry. Additionally the compound was analyzed chemically and physically to find a way to correlate the viscosity with compound composition.