A multivariate optical element (MOE) calculation device is used in an apparatus for determining a property of petroleum in real time flowing in a pipe in petroleum field stream pipes or pipe line. Multiple apparatuses are provided for determining the amount of each of a plurality of properties. An internal reflectance element (IRE) can be used to determine the property of the petroleum from a surface of the petroleum flowing in a pipe. A cleaning apparatus can be provided to clean the surface of the IRE in the pipe and a turbulence generator can be provided in the pipe to insure homogeneity of the petroleum being analyzed prior to analysis. A bellows may be provided in the apparatus housing to compensate for pressure differentials between the housing and the flowing petroleum in the pipe. Various embodiments are disclosed.