| Term | Definition | Formula (if applicable) |
| Total Observed Volume (TOV) | TOV represents the complete volume of material measured within cargo tanks, encompassing all components present during measurement operations. This comprehensive measurement includes cargo oil, free water layers, entrained sediment and water, plus sediment and scale accumulations, all recorded at ambient temperature and pressure conditions. | TOV = GOV + Free Water |
| Free Water (FW) | Free water exists as a distinct phase layer, typically detected through water paste application or interface detection equipment. This separated water layer usually settles at tank bottom areas, though positioning depends on cargo relative density characteristics. Accurate free water measurement proves essential for precise cargo calculations. | |
| Gross Observed Volume (GOV) | GOV calculation involves subtracting free water and bottom sediment from TOV measurements, representing the measured volume of oil and entrained sediment and water at observed temperature and pressure. Practical applications typically calculate GOV without bottom sediment deductions due to quantification difficulties encountered in field conditions. | GOV = TOV - Free Water |
| Gross Standard Volume (GSV) | GSV represents the fundamental measurement reported on tanker operations, calculated by multiplying GOV by the volume correction factor obtained from appropriate ASTM/IP Petroleum Measurement Tables. This standardized volume measurement accounts for oil and entrained sediment and water at standard conditions of 15°C/60°F and atmospheric pressure. ✔ Tip: GSV serves as the primary quantity measured and reported on tankers worldwide, providing standardized comparison capabilities across different operational conditions. | GSV = GOV x VCF (Volume Correction Factor) |
| Sediment & Water (S&W) | Entrained material within oil bulk includes solid particles and dispersed water components, sometimes referenced as base sediment and water (BS&W). This measurement category significantly impacts net volume calculations, particularly for crude oil operations where precision becomes critical for commercial settlements. | |
| Net Standard Volume (NSV) | NSV applies specifically to crude oil operations, calculated by subtracting S&W from GSV to determine 'dry' oil quantity at standard conditions. Product cargoes typically retain S&W within measurements, incorporating these values within receiver quality specifications where appropriate. Sample analysis timing often prevents shipboard NSV calculation due to delayed S&W measurement results. | NSV = GSV x ((100-S&W%)/100) |
| Total Calculated Volume (TCV) | TCV encompasses the complete amount of oil, free water, and S&W reported at standard temperature conditions. Practical calculation involves adding measured free water to GSV figures, providing comprehensive cargo volume accounting for comparison purposes. | TCV = GSV + Free Water |
| ROB (Remaining On Board) | The total amount of material left in cargo tanks, lines, and pumps after the discharge is completed. | |
| OBQ (On-Board Quantity) | The total amount of material (hydrocarbon, water, sediment) in cargo tanks, lines, and pumps before loading operations begin. |
Source: Liquid Cargo Measurement: Understanding TOV, GSV, FW, S&M