"I have had an interest in tracking oil companies (for crude) and refineries (for oil products) trading in their own volume over the past 11 years. As I noted last week (in "Oil Inventories, Speculation, and Hedging"), anecdotal evidence is already emerging that vertically integrated oil companies (VIOCs) – those controlling the upstream/downstream process from field to refinery through retail outlet – were unusually active recently in trading in near-month futures contracts in their own product.
This occurred both when crude oil and gasoline prices were rising (through close on April 29) and thereafter, as crude plummeted almost 15% and gasoline over 13% as of the end of trading on May 6."