Fischer–Tropsch fixed bed synthesis is frequently conducted with a gas recycle and a CO conversion per pass of less than about 60%. In this paper, we have investigated the influence of a gas recycle on the performance of a multitubular reactor (tube length 12 m, diameter 3 cm) for different total CO conversions (X_CO,total) and superficial gas velocities (u_s). The impact of the axial distribution of the intrinsic activity of the Co catalyst in the tubes was also studied. X_CO,total is 95% for the optimal value of u_s of 1 m s⁻¹ combined with a constant activity coefficient C_a of 3 (which equals a Co content of the catalyst of 30 wt%); the conversion per pass is then 45%. Further improvement (X_{CO,per pass} = 47%) is possible by using tubes with two zones of equal length (6 m) and a suitable activity distribution (C_a,1 = 2.5, C_a,1 = 3.5). An activity grading (C_a,mean = 3) with C_a,initial = 2.2 until T_max of 240 °C is reached at z = 2.2 m and then a stepwise rise to C_a of 4 in the remaining 9.8 m leads to X_{CO,per pass} of 49%, the maximum for the given conditions.