Maybe not a "rivalry", but they shared a conference with each other since 1907 (back to the Big 6 and Missouri Valley Conference days), but I see your point.
When the Big 12 conference was formed, OU was at an all-time low and Nebraska was an all-time high. The first year of Big 12 play was 1996, in which OU finished 3-8 and Nebraska was coming off a NC the prior year. But I think the average OU fan lamented the loss of the annual game. We knew...