The physical and chemical properties of oil that need to be tested during trade are critical, as these indicators directly determine the quality of the oil, pricing, transportation safety and refining and processing options. Buyers and sellers will base their settlements on independent inspection reports.These tests can be divided into the following main categories

I. Core pricing indicators (directly affecting prices)

These are the most critical indicators that determine the "goodness" and price of crude oil.

API

API is a measure of the lightness or heaviness of crude oil and is derived from density. the higher the API, the lighter the crude oil. One of the most important pricing factors. Lighter crudes (API > 31.1) are usually worth more because they can be more easily refined into high-value light products such as gasoline and diesel.

Sulfur Content

The percentage of elemental sulfur in crude oil. The other most important pricing factor. Crude oils are classified according to their sulfur content: Low Sulfur Crude Oil: Sulfur content < 0.5%. High value because refining costs are low and environmental requirements are easy to meet. High Sulfur Crude: Sulfur content > 0.5%. Lower value because the refining process requires complex desulfurization equipment, which is costly and corrosive to equipment.

Density/Relative density

The ratio of the mass of crude oil to the mass of the same volume of water at a specified temperature. It is directly related to API degree. Together with the API degree, it reflects the lightness of crude oil and is an important parameter for calculating the weight of cargo.

II. Key quality indicators (affecting refinery value and processing options)

These metrics determine what products the refinery can produce and at what rate.

Stickiness 

Viscosity is a measure of the resistance to flow of crude oil. It affects the pumping and pipeline transportation performance of crude oil. Excessive viscosity increases transportation difficulty and cost.

Pour point and freezing point

 The temperature at which crude oil begins to lose fluidity (pour point) and fully solidifies (freezing point). It is critical for transportation and storage. Crude oil with a high pour point needs to be heated and insulated at low temperatures (e.g., winter or sea transportation) or it will solidify, causing difficulties in loading and unloading or even pipeline blockages, increasing costs and risks.

Salt content 

The amount of soluble chlorides (mainly chlorides of sodium, calcium and magnesium) in crude oil. High salt content can severely corrode refining equipment and must be desalted prior to refining. The price of crude oil with high salt content is reduced accordingly.

Acid Value/Total Acid Value (TAN)

The number of milligrams of potassium hydroxide required to neutralize 1 gram of crude oil reflects the amount of organic acid in the crude. High acid value crude oils are highly corrosive to refinery equipment and require special corrosion-resistant materials and are therefore of lower value.

III. Composition of fractions (determines product yield)

This analysis is done by either real boiling point distillation (TBP) or simulated distillation (SimDis). Crude oil is heated and fractions in different temperature ranges are separated according to the principle that their different components have different boiling points. The ratio of yields of light fractions (e.g., naphtha, gasoline), medium fractions (e.g., kerosene, diesel), and heavy fractions (e.g., heavy oil, asphalt) in crude oil is directly demonstrated. Crude oils with high yields of light fractions are more popular with refiners.

Summarize

In the oil trade, a typical port of embarkation/disembarkation quality inspection report will contain a number of the above indicators. The buyer and seller will compare these test results based on contractually agreed standards (e.g. Platts, API standards, etc.) to:

Determine the benchmark price (based on API degree and sulfur content).

Calculate quality adjustments (premiums or discounts) (based on pour point, acid value, metal content, etc.).

Calculate net weight for final settlement (after deducting moisture and sediment).

Assess the risks and costs of transportation and processing.

Accurate testing of these physical and chemical properties is therefore the basis for fair and smooth international oil trade.

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