A spheroidal olefin polymerization catalyst having a particle size distribution characterized by a Dm*/Dn of less than 3.0, wherein said catalyst comprises: a phosphinimine catalyst, a cocatalyst, and a spheroidal magnesium chloride support; wherein the magnesium chloride support comprises particles with a mass average diameter Dm of 5 to 100 μm, a particle size distribution characterized by a Dm/Dn of less than 3.0, and comprises less than 2% by weight of an electron donor compound; wherein the phosphinimine catalyst has the formula: (L)(PI)MX 2 , where M is Ti, Zr or Hf; PI is a phosphinimine ligand having the formula R 3 P=N-, where R is independently selected from the group consisting of hydrogen, halogen, and C 1 -C 20 hydrocarbyl; L is i) a 1,2 substituted cyclopentadienyl ligand, 1,2-(R*)(Ar-F)Cp, wherein R* is a hydrocarbyl group, and Ar-F is a perfluorinated aryl group, a 2,6 fluoro substituted phenyl group, a 2,4,6 fluoro substituted phenyl group, or a 2,3,5,6 fluoro substituted phenyl group respectively; or ii) a singly substituted indenyl ligand, 1-R ¥ -Indenyl, wherein R ¥ is in the 1-position of the indenyl ligand and is a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or an unsubstituted benzyl group, wherein substituents for an R ¥ alkyl, R ¥ aryl or R ¥ benzyl group may be selected from the group consisting of alkyl groups, aryl groups, alkoxy groups, aryloxy groups, alkylaryl groups, arylalkyl groups and halide groups; and X is an activatable ligand; wherein Dm, Dn and Dm* are determined by the methods set out in the description under the section "Analytical Measurements". wherein the magnesium chloride support comprises particles with a mass average diameter Dm of 5 to 100 μm, a particle size distribution characterized by a Dm/Dn of less than 3.0, and comprises less than 2% by weight of an electron donor compound; wherein the phosphinimine catalyst has the formula: (L)(PI)MX 2 , where M is Ti, Zr or Hf; PI is a phosphinimine ligand having the formula R 3 P=N-, where R is independently selected from the group consisting of hydrogen, halogen, and C 1 -C 20 hydrocarbyl; L is i) a 1,2 substituted cyclopentadienyl ligand, 1,2-(R*)(Ar-F)Cp, wherein R* is a hydrocarbyl group, and Ar-F is a perfluorinated aryl group, a 2,6 fluoro substituted phenyl group, a 2,4,6 fluoro substituted phenyl group, or a 2,3,5,6 fluoro substituted phenyl group respectively; or ii) a singly substituted indenyl ligand, 1-R ¥ -Indenyl, wherein R ¥ is in the 1-position of the indenyl ligand and is a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or an unsubstituted benzyl group, wherein substituents for an R ¥ alkyl, R ¥ aryl or R ¥ benzyl group may be selected from the group consisting of alkyl groups, aryl groups, alkoxy groups, aryloxy groups, alkylaryl groups, arylalkyl groups and halide groups; and i) a 1,2 substituted cyclopentadienyl ligand, 1,2-(R*)(Ar-F)Cp, wherein R* is a hydrocarbyl group, and Ar-F is a perfluorinated aryl group, a 2,6 fluoro substituted phenyl group, a 2,4,6 fluoro substituted phenyl group, or a 2,3,5,6 fluoro substituted phenyl group respectively; or ii) a singly substituted indenyl ligand, 1-R ¥ -Indenyl, wherein R ¥ is in the 1-position of the indenyl ligand and is a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or an unsubstituted benzyl group, wherein substituents for an R ¥ alkyl, R ¥ aryl or R ¥ benzyl group may be selected from the group consisting of alkyl groups, aryl groups, alkoxy groups, aryloxy groups, alkylaryl groups, arylalkyl groups and halide groups; and X is an activatable ligand; wherein Dm, Dn and Dm* are determined by the methods set out in the description under the section "Analytical Measurements". <EOS>