The best technique for the detection of oil or any other liquid, whether surface or deep is through calculation of attenuation coefficient, which is calculated by the following equation:
Att. C. = (f * Vs(Gmax))/V1
Please note that the best modern technique that give clearly and excellent imaging and explanation for this coefficient is the " New Applied and Innovative Mathematical Theory in Seismology, Geophysics and Geotechnical ", which is exist in ResearchGate by the following link:
I assume you mean water depth of 200 m. I don't know if you are looking for droplets or dissolved oil constituents or gases.
Emulsifed oil is off the table, as it is a surface phenomena.
During the DWH oil spill, fluorescence was used, see the intercalibration report by Conmy et al (2014). This identifies oil but not a specific oil. My guess is you are more interested in this.
You can also look at Camilli et al (2010), particularly the supplementary materials.
LISST is popular, when combined with techniques to identify the particles as oil, such as holography. http://www.sequoiasci.com/product/lisst-100x/