This paper presents a complete set of friction factor correlations for both Newtonian and non-Newtonian fluids in laminar and turbulent flow in coiled tubing. The friction factor correlation for non-Newtonian fluids in laminar flow is obtained based on theoretical analysis and numerical solutions of the flow equations of a power-law model fluid in curved pipes. The empirical correlation for non-Newtonian fluids in turbulent flow is developed based on full-scale experiments of polymeric fluid systems in various 1", 1–1/2", and 2–3/8" coiled tubing reels. To consider the effect of pipe roughness in coiled tubing, a modified correlation is proposed by combining the Srinivasan et al. correlation for smooth curved pipe and the Chen correlation for rough straight pipe. Examples are given to illustrate the applications and accuracies of the newly developed correlations.