Single-phase and two-phase frictional pressure drop in horizontally oriented double helically coiled tubes confined in a cylindrical shell are experimentally studied using an instrumented test loop that represents a prototypical liquified natural gas (LNG) fuel delivery system for internal combustion (IC) engines. Adiabatic experimental data addressing liquid (water) and gas (nitrogen) single-phase flows, as well as two-phase flows (air–water) in the helicoidally coiled tubes are presented. The range of Reynold numbers for single-phase flow experiments is 2600–4800. In two-phase flow experiments, the only liquid and only gas Reynolds numbers varied in 1030–6600 and 1700–17700 ranges, respectively. In a laminar single-phase flow regime, the measured friction factors are in relatively good agreement with well-established correlations. In the turbulent flow regime, the measured friction factors are moderately higher than the prediction of well-established published correlations. Two-phase flow frictional pressure drops are compared with some relevant correlations, with the poor agreement. The generated experimental data are empirically correlated based on the two-phase flow multiplier concept.