I've always found Oblivion really quick. Practically walk on. I usually go round twice as it's such a short wait.
I've been single rider on oblivion a few times with mixed results. I love single rider queues they're usually SO much quicker and save long waits surrounded by groups of people if your on your own. You may also find yourself talking to other single riders and having a fun day out!
Anyway, back to oblivion, about a month back I went to single rider oblivion and it was the longest queue I have ever seen, the main queue was nearly at the entrance to the queue and queued all the way up the slope, and the single rider queue started just after where single riders and fast trackers join separate queues. It took about an hour and standing there on your own for that amount of time with hardly any movement was a killer, especially when I know that most of the time it's walk on.
One time when I Did single rider 13 they just let all the single riders have a train to themselves, there was about a half an hour main queue too