Stewart,
Are you going to do the Gibb river road? if so you can get fuel at Derby,Mt Barnett Roadhouse(Manning Gorge) Drysdale Station (if heading to Mitchell Plateau or Kalumburu) Mt Elizabeth and Kalumburu. If continuing on to Wyndham ,pretty sure you can get fuel at Home valley and El Questro.
Take a few jerry cans of diesel and a full tank and you should be right.The only place you would likely get into trouble up that way on the Gibb is maybe the Mitchell Plateau.It's off the beaten track so maybe a sat phone would be good insurance.Other than that you should be right, there's that much traffic up there now you would only be stranded a few hours.......but be prepared.
The 1st time i did the gibb back in April 91 was in a Avis triton ute with the camping pack,,got all the way up to Mitchell and Kulumburu and all the way back again over 2 weeks and did 1 tyre(20km's out of Derby on the tar).The triton was trashed but did well.