As per Maxol's FAQ section on maxol.ie
What is the Octane Rating of E5 compared to ordinary Unleaded ?
The Octane Rating of Ordinary unleaded ranges from 95.0 to 95.9 - average 95.5. The Octane rating of E5 averages 99.2
What is the Energy Content (Calorific Value) of E5 compared to ordinary Unleaded Petrol?
One litre of Unleaded has a calorific value of 31 MJ.
One litre of Bioethanol has a calorific value of 21.2 MJ.
One litre of E5 has a calorific value of 30.51 MJ.
One litre of Unleaded emits 2.36 kg of CO2.
One litre of Bioethanol has a calorific value of 21.2 MJ.
What's the difference in Carbon Emissions between ordinary Unleaded and E5?
One litre of Unleaded emits 2.36 kg of CO2
One litre of ethanol emits: ((2.36/31)*21.2)*0.5 = 0.81 kg CO2.
One litre of E5 emits: (0.81*0.05) + (2.36*0.95) = 2.28 kg CO2.
(5% ethanol : 95% petrol)
The difference in emissions between one litre of Unleaded and one litre of E5 is thus estimated to be 3.4%.
Full FAQ Here
http://www.maxol.ie/e5/q&a.html