Saudi drops WTI oil contract, use Argus Sour Crude Index instead.

From this FT article: "Saudi drops WTI oil contract", Saudi Arabia will use Argus Sour Crude Index instead.

What is this Argus Sour Crude Index ?
I did a search on Argus Media which created the index.
Found this PDF file: Argus Sour Crude Index.

We can see the methodology and specifications from this file (details and examples of calculations are illustrated).

This Argus Sour Crude Index (ASCI) calculation method has some interesting features..

Argus Sour Crude Index (ASCI): daily volume-weighted average of aggregate deals of components grades: Mars, Poseidon, Southern Green Canyon (SGC).
It claims to be "a pricing tool designed to serve primarily buyers and sellers of imported crude that need a broader index of US Gulf coast medium sour crude value for use in long-term contracts".

Argus Sour Crude Index Price = Argus Sour Crude Index Differential + same month WTI Formula Basis

WTI Formula Basis: pricing series by combining Nymex futures (before expiry) and WTI spot prices (after expiry), to represent mean of WTI Cushing spot assessment for 3 business days after expiry which precede pipeline scheduling.

This "normal" calculation method (daily volume-weighted average of aggregate deals of Mars, Poseidon, SGC) is to be used if combined volumes of all 3 grades reach "volume minimum" (6000 barrels per calendar day).

If volume minimum is not reached, then "Proportional Assessment" is to be used.

Proportional Assessment:
Beginning of every trade quarter, Argus will average volume of trade in each of last six trade months and assign each grade a % of traded volume (for example 71% Mars, 22% Poseidon, 7% SGC).
ASCI will be constructed using individual volume-weighted average prices for Mars, Poseidon and SGC using the % (for example 71% Mars, 22% Poseidon, 7% SGC).

To address difficulties associated with "stream disruptions" (output from pipeline ceases, market for that grade becomes illiquid), there is this "Intelligent Assessment".

Intelligent Assessment
If stream disruptions happen (1 grade becomes illiquid), Argus will assesses and decides whether to suspend daily price or continue with Intelligent Assessment.
If trade in remaining 2 grades > volume minimum, index will be calculated from the remaining 2 grades. If remaining 2 grades < volume minimum, then the "proportional assessment" will be applied in the same proportion, using Argus published prices for the grades (actual trade or intelligent assessment). If all streams are very disrupted until integrity of index damaged, Argus will consult with industry to form an alternative index (other sour grades, import values, intelligent assessments).

My summary:
1. ASCI uses both futures and spot price to try to arrive at a better price representation.
2. ASCI uses past volume% to calculate index if current trade volume is low (i.e. illiquid; demand low, supply intact).
3. ASCI calculation takes away grade with stream disrupted (i.e.: illiquid; demand intact, supply disrupted).
4. ASCI is still using WTI, Nymex to arrive at its data. It is still dollar-denominated.
5. ASCI is volume-weighted; uses deal volume when market is normal, uses past volumes when overall market is "illiquid" (volume low). Volume weighted "price" may be more representative than, say, closing price.

Basically, it’s trying to have a better price representation (against fluctuations, manipulations, distortions etc)... We can also guess this from its claim: "a pricing tool designed to serve primarily buyers and sellers of imported crude that need a broader index of US Gulf coast medium sour crude value for use in long-term contracts".