The definition of "petroleum" according to Chambers 21st century dictionary is: "A naturally-occurring oil consisting of a thick, dark liquid mixture of hydrocarbons, distillation of which yields a wide range of petrochemicals, e.g. liquid and gas fuels, asphalt and raw materials for the manufacture of plastics, solvents, drugs etc."

Under "oil", the second definition is "petroleum".

"Petroleum" is therefore synonymous with "crude oil", since the latter is also unrefined...but I've only ever heard "oil prices" as an expression; I don't think anyone uses "petroleum prices", though I do stand to be corrected.