It seems like it is not a petrol shortage per se. It seems like it is a distribution problem due to a lack of truck drivers. They have the petrol and just cannot get it to the pumps. Apparently there are plans to use drivers from the military to relief that problem.
Some pubs also have a distribution problem with beer. The commonwealth citizen Slim Dusty performed a song about that: https://www.youtube.com/watch?v=7cKPchRDaVM . As a funny coincindence rumor has it that the reason was a transportation failure as well: https://www.youtube.com/watch?v=KkDUBYOzyAQ
Got to love the Aussies for creating fitting songs decades ago.