ISO 3838:2004 specifies methods for the determination of the density or relative density of crude petroleum and of petroleum products handled as liquids.

The capillary-stoppered pyknometer method is also for use with solids and this method may also be used for coal tar products, including road tars, creosote and tar pitches, or for mixtures of these with petroleum products. This method is not suitable for the determination of the density or relative density of highly volatile liquids having Reid vapour pressures greater than 50 kPa according to ISO 3007 or having an initial boiling point below 40 degrees Celsius.

The graduated bicapillary pyknometer method is recommended for the accurate determination of the density or relative density of all except the more viscous products, and is particularly useful when only small amounts of samples are available. The method is restricted to liquids having Reid vapour pressures of 130 kPa or less according to ISO 3007 and having kinematic viscosities less than 50 mm²/s (50 centistokes (cSt)) at the test temperature.

Special precautions are specified for the determination of the density or relative density of highly volatile liquids.