Methods for gas phase olefin polymerization are provided. The method can include combining a spray dried catalyst system with a diluent to produce a catalyst slurry. The catalyst system can include a metallocene compound. Ethylene, a continuity additive, and the catalyst slurry can be introduced to a gas phase fluidized bed reactor. The reactor can be operated at conditions sufficient to produce a polyethylene. The spray dried catalyst system can have a catalyst productivity of at least 12,000 grams polyethylene per gram of the catalyst system.