Light, Heavy, Sweet or Sour?

As the famous Castrol advertisement suggests: Oils ain’t oils! There are big differences between light and heavy crude oil and it can also be sweet or sour as well.

Crude Oil, or “petroleum” as it is also called is the raw material found in the ground. Petroleum is actually a Latin word, showing how long humans have used it! To help distinguish between light and heavy the American Petroleum Institute (API) defines a gravity reading to describe light and heavy crudes.

To complicate things further, oil is also named after it’s geographical location. Examples of this are Brent Sweet Light Crude from the North Sea and the West Texas Intermediate (or Texas Sweet Light as it is often referred to).

So lets go through the 4 types of oil and their usage.

Light Crude has a low wax content and can move freely at room temperature. The API gravity reading for light crude is higher than 33° and typically is over 40°. North Sea oil is a light crude.

Heavy Crude has a high wax content and the API gravity reading is less than 28° and typically less than 20°. The largest reserves of heavy oil are in Venezuela and have an API reading of just 10° although the tar sands of Canada come close. The other main countries producing heavy oils are Iraq and Russia. Heavy crude requires more refining which means it costs more to convert to a usable product. This is a factor in why the Russian economy is struggling at the moment – they will get less per barrel in profit due to the higher production costs, so they are desperate for the crude oil price to stop its downward slide and start rising again.

Sweet Crude has a sulphur content of less than 0.5%. Sweet crude oil contains small amounts of hydrogen sulfide and carbon dioxide. Sweet crude is mostly used for refining into gasoline, kerosene and diesel. Sweet light crude is the most preferred choice as it requires less refining, therefore it is quicker and cheaper to get to market. Sweet crudes come from areas such as Texas, Louisiana, Libya and Indonesia.

So, if heavy oil is the opposite of light oil, then it doesn’t take a genius to realise that Sour Crude is the opposite of Sweet! Sour crude has a higher sulphur content and as such needs an intermediate step to stabilise it before it is pumped into sea going tankers. Sour crude is the most dangerous oil due to it’s high content of hydrogen sulphide and can be fatal if handling precautions aren’t taken. Sour crude typically comes from South America and the Middle East.

Roughly 84% of the hydrocarbons in crude oil are converted into fuels such as gasoline, diesel and kerosene, the remaining 16% are used in chemical processes for pharmaceuticals, plastics, solvents and fertilisers. Crude oil will remain an important fuel for humans for many years to come, even with an ever larger fleet of electric, hybrid or hydrogen cars on the roads.