The 1991 WAFL season was the 107th season of the various incarnations of the West Australian Football League. With the West Coast Eagles still pushing attendances down and club finances into the red, the league made further experiments. Following on from the VFL and SANFL it introduced a "final five" to replace the final four in use since 1905, but this did not produce the hoped-for financial benefits and was abandoned after four seasons. A more enduring result of this chance was a "double-header" system of playing finals, whereby the two senior semi-finals were played at Subiaco Oval on the same day, with the first game starting just before noon and the second at the traditional time for playing finals. As a consequence of the double-headers, reserves finals were played at Fremantle Oval and colts at Bassendean.