As ny59giants already said, you don't have enough tankers, but you have far more xAKs as you need. For the japanese players, using AKs isn't recommend due its bad "real" fuel gain, but as allies, you won't run out of fuel and xAKs.
In '42 and only against the AI(!), i always have 6 fuel convoys running to australia:
1 from Colombo (filled with fuel from Abadan) to Perth using fast tankers and 2 AMCs and 2 DDs as escorts (plotted close to map border)
1 from West Coast or Pearl to Sydney with Tankers/AOs, 1 CA or modern CL and 4 DDs as escourts (plotted far below Suva)
3 from West Coast or Pearl to Sidney with xAKs, 1 old CL and 2 DM/DMS as ecorts (plotted below Suva)
1 from Cape Town to Perth using xAKs with additional liquid storage (dutch ones i think?) with DDs or AMs as escorts (Cape Town is refueled from East Coast using CS-Convoys).
Use of West Coast or Pearl depends on use of Pearl, fuel status etc. I often decide again from convoy to convoy.