Naphtha boiling range compositions are provided that can have improved combustion properties (relative to the research octane number of the composition) in spark ignition engines and/or compression ignition engines. The improved combustion properties can be achieved by controlling the total combined amounts of n-paraffins and isoparaffins that include a straight-chain propyl group (R1—CH2—CH2—CH2—R2). For such a straight-chain propyl group, R2 can correspond to any convenient CxHy group that can appear in a paraffin or isoparaffin. R1 can correspond to a hydrogen atom, making the straight-chain propyl group a terminal n-propyl group; or R1 can correspond to any convenient CxHy group that can appear in a paraffin or isoparaffin.