25 Dollars - Elizabeth II 4th Portrait - Koala - Platinum

Australia's platinum Koala series began in 1987, making Perth one of the earliest sovereign mints to issue a platinum bullion program in direct competition with the Canadian Maple Leaf. The 1999–2000 issues coincide with the transition to Ian Rank-Broadley's effigy of Elizabeth II, which first appeared on Australian coinage in 1999 — the fourth and final portrait used during her reign on Perth Mint bullion before subsequent refinements.

Platinum spot prices collapsed through much of 1999, briefly falling below gold — a rare inversion that suppressed collector premiums on platinum issues from this period at time of release.