Unleaded blend composition having a Motor Octane Number (MON) of at least 80 having less than 42% of aromatic compounds, and at least 2% by volume of the total composition of component (a′), which is a substantially aliphatic hydrocarbon refinery stream of MON value of at least 85. At least 70% in total of the stream is branched chain alkanes, the stream being obtained by distillation from a refinery material as a cut having Initial Boiling Point of at least 15° C. and Final Boiling Point of at most 160° C. The Boiling Points are measured according to ASTMID2892. At least 5% of at least one paraffin, aromatic hydrocarbon compound or olefinic hydrocarbon has a bp 60-160° C., with not more than 5% of the total composition of hydrocarbon having a bp more than 160° C. Less than 5% 2,2,3-trimethylbutane or 2,2,3-trimethylpentane is present.