We describe an algorithm for the analysis of color images of basins which gather dirty water, with the objective of detecting and estimate the presence of exceeding combustible oil. The algorithm first detects most of the pixel corresponding to the combustible oil applying a thresholding method based on the entropy of the image's histogram. Then it treats the images differently according to the first order statistics of the image's hue; we distinguished two cases in which the algorithm has a different behavior: in the first case, it applies a clustering method in the HSV color space, whereas in the second case it operates in the CIE-L*a*b* color space. Finally it estimates the percentage of the present oil.