Usan Crude Oil: 2025 Assay, API Gravity & High Acidity

API gravity: 27.4°¹
Sulphur: 0.29 wt%
Acidity (TAN): 1.65 mg KOH/g
Pour point: -77 °C
Barrels per tonne: 7.07 derived²
Standard cargo: 1,000,000 bbl³

Evidence basis: Company-reported Company-published assay, dated 21 February 2025. Crude quality varies from cargo to cargo; in any transaction the certificate of quality for the specific lifting governs, not a published assay.

Data limitation

The pour point of −77 °C is reproduced exactly as printed in the assay; it is unusually low and should be confirmed against a cargo certificate.

Usan: quality and origin

Usan is a deepwater crude produced about 100 km offshore. Reference tables commonly list it at 30–31° API and about 0.25% sulphur.³⁴ The most recent company assay, published by ExxonMobil and dated February 2025, is materially different: 27.4° API, 0.29% sulphur and a total acid number of 1.65 mg KOH/g, with acidity of 2.3–3.3 in the heavier distillate cuts.¹

Why acidity matters

A total acid number above about 1 places a crude in the high-acid category, which can cause naphthenic-acid corrosion in refinery units not built with suitable metallurgy. In our reading, Usan is therefore a specialist grade: refiners able to handle or blend high-acid crude may find value in it, while others should check unit limits before bidding. The same assay reports nickel at 16.6 and vanadium at 3.9 parts per million — higher than most Nigerian grades — and 39.4% residue above 370 °C.¹

Cargoes and buyers

Usan trades in one-million-barrel cargoes.³ Indian Oil Corporation bought a Usan cargo by tender in 2025 according to Reuters reporting.⁵ Reported output was 32.23 thousand b/d in May 2026.⁶

Distillation yields

Yields in vol% as published. Source: ExxonMobil, assay dated 21 February 2025.
Cut	Yield (vol%)
C5–65 °C	3.5
65–100 °C	4.3
100–150 °C	7.7
150–200 °C	8.1
200–250 °C	9.6
250–300 °C	10.9
300–350 °C	10.9
350–370 °C	4.1
370 °C+ residue	39.4
of which 550 °C+	12.2

Other assay values: density 890.1 kg/m³; viscosity 22.2 cSt at 20 °C; 10.7 cSt at 40 °C; nickel 16.6 and vanadium 3.9 mg/kg.¹

How published figures compare

Publishers quote different qualities for Usan because assays are run years apart on a stream whose field mix changes, and because price-reporting agencies publish rounded "typical" values. We show the figures side by side rather than silently choosing one.

Source	API	Sulphur wt%	Evidence
ExxonMobil, 21 February 2025¹	27.4	0.29	Company-reported
Argus typical, Aug 2026³	30.6	0.23	Industry
EIA table, Nov 2025⁴	31	0.25	Government

Loading, operator and output

Loading point: Usan FPSO — see the export terminal database
Operator: Operatorship not confirmed by us from a current primary source; the assay is published by ExxonMobil as an equity holder. OML 138.¹
Producing area: Deepwater, about 100 km offshore in 750–850 m of water
Status: Active
Reported output: 32.2 thousand b/d — USAN stream, May 2026.⁶ This is production by stream, not exports; part of some streams is delivered to Nigerian refineries.
Pricing basis: A differential to Dated Brent — see how Nigerian crude is priced
Volume conversion: 7.07 barrels per tonne at this gravity (our derived figure) — the barrels-to-tonnes converter has Usan as a preset
Checking an offer: A genuine Usan cargo traces back to the operator and loading point above. See who can lawfully sell Nigerian crude and the verification centre before engaging any seller

Comparable grades

The Nigerian grades closest to Usan by API gravity. The comparison tool puts any of them side by side.

Egina27.3° API0.17% sulphur · Medium sweet Bonga27.7° API0.26% sulphur · Medium sweet Nembe29° APIMedium sweet (new grade, 2023)

Usan crude oil