How can you find the current enterprise value ev for a for barrel of oil?

No.

Enterprise value refers to a measure of a company's worth. Oil prices will vary depending on the quality of oil and demand for at any time. Oil companies actively sell their crude oil to a worldwide market, and the price can change from minute to minute. Their negotiated sales price is not public information.

However, the "furtures contract" selling price of a set of similar crude types, referred to as a basket of crudes , (West Texas Light, for example) can be very easily identified from the commodities market prices (see related link) and is a good proxy to study the trend of actual contracted prices.