An efficient manufacturing process for .alpha.-olefins using certain iron containing ethylene oligomerization catalysts, comprises one or more liquid full reactors which are approximately at the bubble point of reacting ethylene, and optionally a final reactor which is at a lower pressure than the first reactor, both operating under other specified conditions. This process minimizes both the capital and operating costs for the plant. The .alpha.-olefins produced are useful as monomers for polymers and as chemical intermediates, for example for making detergents.