A process for producing bimodal polyethylene resins in two reactors in series, the process comprising producing a first polyethylene resin fraction in a first slurry loop reactor in a diluent in the presence of a catalyst and producing a second polyethylene resin fraction in a second slurry loop reactor, serially connected to the first reactor, in the diluent in the presence of the catalyst, the first polyethylene resin fraction being passed from the first reactor to the second reactor together with the catalyst, one of the first and second reactors producing a resin fraction of higher molecular than the resin fraction produced by the other of the first and second reactors, characterised in that the first reactor is fed with a feed of ethylene and diluent having an ethylene content of at least 70 wt % based on the weight of the diluent and in that in the first reactor the slurry of polyethylene in the diluent has a solids content of at least 30 wt % based on the weight of the diluent.