A method and apparatus is provided for determining OBM filtrate fraction in a downhole fluid sample. One embodiment of the method is used when there is significant difference between the coloration of formation fluid and the coloration of OBM filtrate. Another is used when there is little or no difference...http://www.google.com.au/patents/US6274865?utm_source=gb-gplus-sharePatent US6274865 - Analysis of downhole OBM-contaminated formation fluid
