What is density? Density is a physics degree of consistence measured by the quantity of mass per unit volume. It is one of the physics indices of the chemical material. Density is not the index to specify the physical properties of oil and oil products as organic blends. It is the value to convert volume to mass taking into consideration thermal expansion. That is why only some of the oil products are density regulated though it is a quality index. Since liquids’ density is always recorded, all the products are tested for density. However, the volume of most of the materials varies with temperature (there exists a temperature related expansion coefficient to determine how many times the volume increases at 1 degree increment of temperature). For volume conversion into mass it is necessary to take into consideration the temperature of the liquid measured. If the temperature is different from the reference temperature, then the temperature related expansion coefficient value is entered in the formula. The density of any oil products depends upon their composition and temperature, besides it is a variable. Only individual oil products are regulated for oil product composition (propane or butane). Other oil products are not regulated because more than 200 different compounds are there in the composition of gasoline, kerosene (jet fuel) and diesel fuel, and there is not any direct relation between the composition and specific performance properties. Oil product density Oil product density is measured at a reference temperature or the conversion calculation is performed. Gasolines A-92, A-95 — 0,725–0,780 kg/l, at 15°C; Diesel fuel — 0,820–0,845 kg/l, at 15°C; Density is specified in the Quality Certificate of each shipment of the product and it shows how many litres are there in a ton. This is determined by dividing kilogram by density to find out how many litres there are in a kilogram; the achieved figure times one thousand shows how many litres there are in a ton. It is necessary to consider the temperature because all the materials are subject to expansion coefficient: the higher the temperature the lower the density is (consequentially the more litres are).