Octane Blending Indices

Research (RON) and motor (MON) octane blending values for gasoline pool components, plus sensitivity and volatility notes.

Pure Component RON-MON

Octane Blending Indices & Pure Component RON/MON · Refs: API TDB Ch.2; Gary/Handwerk Ch.10; ASTM D2699/D2700; Meyers' Handbook

Component	RON	MON	(R+M)/2	BON (RON)	BON (MON)	Notes
n-Butane	94	89.1	91.5	113	113	Reid vapor pressure booster
i-Butane	102	97.6	99.8	122	122	Alkylation feed
n-Pentane	61.7	61.9	61.8	62	67	Low octane paraffin
i-Pentane	92.3	90.3	91.3	93	95	LSR component
n-Hexane	24.8	26	25.4	19	22	Poor octane
2,2,4-Trimethylpentane	100	100	100	100	100	Isooctane - reference standard
Benzene	100	91.2	95.6	115	108	Limited by EPA 0.62 vol% cap
Toluene	124	112	118	115	103	Reformate aromatic
p-Xylene	146	127	136	146	127	Gasoline octane contributor
m-Xylene	145	124	134	145	124
o-Xylene	120	103	111	120	103
Ethylbenzene	124	107	115	124	107
1-Hexene	76.4	63.4	69.9	96	87	Olefin
Cyclohexane	83	77.2	80.1	83	77	Naphthene
Methylcyclohexane	74.8	71.1	73	87	88	Reformer feed
Methanol	133	99	116	134	94	M85/M100 fuel
Ethanol	109	90	100	122	99	E10/E85
MTBE	118	101	110	118	101	Banned in some states
ETBE	118	102	110	118	102
TAME	111	98	105	112	99	Tert-Amyl Methyl Ether
DIPE	110	96	103	112	97

Refinery Streams

Typical Refinery Gasoline Blend Stream Octanes · Gary/Handwerk 6th ed. Table 10-2; typical ranges

Stream	RON (typ)	MON (typ)	R+M/2	Notes
Butanes (n+i mix)	94	91	93	Octane boost, RVP
LSR Naphtha (C5-180F, virgin)	68	67	68	Feed to isomerization
HSR Naphtha (180-380F, virgin)	48	46	47	Feed to reformer
Reformate (90 RON severity)	90	81	86	Semi-regen CCR
Reformate (100 RON severity)	100	88	94	Max aromatics
FCC Gasoline (full range)	92	80	86	Olefinic - sulfur
FCC LCN (light cat naphtha)	92	82	87
FCC HCN (heavy cat naphtha)	89	79	84
Alkylate (HF or H2SO4)	95	92	94	Clean, low RVP, low S
Isomerate (C5/C6)	86	83	85	Good RVP trade
Polymer Gasoline	95	82	89	Olefinic, historical
Coker Naphtha (full range)	70	65	68	Needs hydrotreat + iso
Hydrocrackate (heavy)	80	78	79	Low octane, good diesel
Ethanol denatured (E100)	109	90	100	BOV boost w/ volatility

Blending Methods

Octane Blending Methods · ASTM D2885; Meyers' Handbook Ch. 12; Ethyl Corp TRBN

Volume-average	Simplest; ON_blend = sum(xi * ONi). Works poorly for aromatics and oxygenates.
Weight-average	ON_blend = sum(wi * ONi). Closer to reality for high-density streams but still imprecise.
Ethyl RT-70 (TRBN)	Published Ethyl Tech Service RT-70 curves. Still used for rough checks.
Mobil Method (BONs)	Each component has BON_RON and BON_MON that blend linearly on volume. Most refinery LP models use this.
Interaction terms	HiTech RBOB blending adds interaction coefficients (e.g., aromatic * olefin term). Vendor-proprietary.
Rule of thumb - sensitivity	Sensitivity S = RON - MON. Parrafins S~0; Aromatics S=10-25; Olefins S=8-15. Spec often limits S<10 for FC.
Rule of thumb - octane giveaway	Every 1 ON of giveaway on a 100 kbd pool = ~$0.5-1.5M/yr depending on spread.

Source: Octane_Blending_Indices_Reference_v1.xlsx

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