On-Board Quantity / Remaining On Board
Abbreviation: OBQ / ROB
OBQ is the oil, water, and sediment in a tanker's cargo tanks before loading; ROB is what remains after discharge. Both are gauged to establish the true quantity transferred.
Quick facts
- OBQ
- Before loading
- ROB
- After discharge
In practice
The cargo officer gauges OBQ before loading and ROB after discharge, using a wedge formula for thin layers over a trimmed tank bottom. Large or unexpected ROB is documented with samples and, where a shortage is alleged, backed by a letter of protest and the ship's stripping records.
Regulatory detail & full definition
On-Board Quantity (OBQ) is the total of oil, water, and sediment already present in a tanker's cargo tanks and lines before loading begins; Remaining On Board (ROB) is the equivalent quantity left after discharge is complete. Both are measured by gauging each tank (often including a wedge calculation for small quantities lying over the tank bottom when the ship is trimmed by the stern) and are reported on the ullage report and in the cargo documentation. OBQ and ROB matter because they bracket the voyage: subtracting OBQ from the loaded figure, and accounting for ROB at the discharge port, establishes the quantity actually transferred and separates genuine cargo from clingage, non-pumpable oil, water, and sediment. Well-documented OBQ and ROB — witnessed where possible by an independent surveyor — protect the ship against inflated short-delivery claims, and unusually large ROB can indicate heavy or waxy crude, a cargo-heating problem, or stripping difficulties that should be recorded and, if disputed, protested.
Authoritative source: API — Manual of Petroleum Measurement Standards ↗
Related
Source: Tanker custody-transfer practice (API MPMS)
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