Parallel lines of PRR between Tryonville & Titusville

I notice that several old maps show the PRR with two parallel lines between Tryonville and Titusville PA, and two show these extending south to Petroleum Center.

I know that one of the predecessors, "Oil Creek RR" was 6' gauge, so I wonder if this is the reason for the duplication. If so, how far south did the 6'g tracks get?

(I also put this on the PRR forum.)

I believe the predecessor lines were the "Oil Creek Railroad", which you have already mentioned, that ran from Oil City north, through Titusville, to Corry where it connected with the Buffalo, Corry & Pittsburgh. The other parallel line appears to have been the Union and Titusville that ran from Union City southeast, through Titusville and on to Oil City. The U&T and OC were on opposite sides of Oil Creek (the waterway) until the U&T crossed the Oil Creek at a point south of Petroleum Center.