A multi-lateral well completion system segregates and prevents commingling of the production fluids flowing from a plurality of lateral wellbores which extend outward from a main wellbore. The system includes a segregator body member that is positioned and oriented in the main wellbore adjacent the inner ends of the lateral wellbores in a manner such that the inlets of separate, longitudinal flow passages in the segregator body member are aligned to receive the production fluid flow from respective lateral wellbores. Various structures are disclosed which provide isolated, pressure-sealed communication between the inner ends of each lateral wellbore and the flow passage inlet that is aligned therewith. Each flow passage in the body member can be equipped with a remotely operated valve to control production fluid flow therethrough, as well as with sensors to monitor various characteristics of the production fluids. Gas lift of the production fluids also can be provided.