If you mean the analysis of chlorine gas in hydrocarbon based oil, then it is very difficult because the chlorine oxidizes the oil very quickly. In fact, there have been explosions caused by chlorine reacting with oil in valve packings.
If mineral oil has been exposed to small amounts of chlorine, the oil will go black very quickly due to oxidation. The chlorine will normally be converted to chloride.
A simple qualitative test you may consider is to wash the oil with DI water, slightly acidify the water with nitric acid if necessary, and add silver nitrate dropwise to the water and check for turbidity (silver chloride). Visible turbidity is normally seen at 3 ppm and higher chloride. If you need quantitative analysis, ion selective electrode analysis of the water wash is usually sufficient and is relatively inexpensive.
Ion chromatography is another more expensive, but higher performing method for analyzing chloride in the water wash.