Designs.
Fisher, P. H.; Penttila, Tim; Royle, Gordon F. Symmetric designs, polarities and sub-designs. Discrete Math. 71 (1988), no. 1, 19--32.
Fisher, P. H.; Penttila, Tim; Praeger, Cheryl E.; Royle, Gordon F. Inversive planes of odd order. European J. Combin. 10 (1989), no. 4, 331--336.
Fisher, P. H.; Penttila, Tim One-point extensions of polar spaces. European J. Combin. 11 (1990), no. 6, 535--540.
O'Keefe, Christine M.; Penttila, Tim; Praeger, Cheryl E. Block-transitive, point-imprimitive designs with $\lambda=1$. Discrete Math. 115 (1993), no. 1-3, 231--244.
Penttila, Tim One-point extensions of finite inversive planes. Australas. J. Combin. 8 (1993), 53--54.
Nickel, Werner; Niemeyer, Alice C.; O'Keefe, Christine M.; Penttila, Tim; Praeger, Cheryl E. The block-transitive, point-imprimitive $2$-$(729,8,1)$ designs. Appl. Algebra Engrg. Comm. Comput. 3 (1992), no. 1, 47--61.
O'Keefe, Christine M.; Penttila, Tim; Praeger, Cheryl E. Block-transitive, point-imprimitive designs with $\lambda=1$. Discrete Math. 115 (1993), no. 1-3, 231--244.
Penttila, Tim One-point extensions of finite inversive planes. Australas. J. Combin. 8 (1993), 53--54.
Graphs.
Penttila, Tim; Royle, Gordon F. Sets of type $(m,n)$ in the affine and projective planes of order nine. Des. Codes Cryptogr. 6 (1995), no. 3, 229--245.
Ivanov, A. A.; Liebler, Robert A.; Penttila, Tim; Praeger, Cheryl E. Antipodal distance-transitive covers of complete bipartite graphs. European J. Combin. 18 (1997), no. 1, 11--33.
De Clerck, Frank; Hamilton, Nicholas; O'Keefe, Christine M.; Penttila, Tim Quasi-quadrics and related structures. Australas. J. Combin. 22 (2000), 151--166.