Years ago there was a guy driving around Australia in an old Diesel van painted with pictures of vegetables on it and the words "VegeVan". in the back he had some equipment for making BioDiesel from the left over oil from takeaway/ Fish and chip shops. He would pull over in shopping centres, go into takeaway shops collecting the used cooking oil from anyone that would give it to him. Then try show anyone interested his setup saying this is how we save the planet. I saw it a few times while riding my bike to work and it smelt like old fish and chips, not great but better than the typical old diesel van blowing black smoke.

I googled BioDiesel back then and couldn't find much about it apart from on article in a newspaper that the UK had just banned the backyard manufacture of BioDiesel until they work out a way to tax it. So not sure how that went.

Now BioDiesel is available for sale in Australia but not much cheaper than regular, i think there are hardly any people making it themselves and the commercial places selling it are probably paying taxes just like regular diesel. Not sure if that is because it is banned or just not worth doing. As a petrol car owner I never really looked into it.

I did read that the tax collected on petrol has reduced over the years, we are driving more than ever but in cars that are now doing say 7L/100km compared to 12L/100km, My 1968 mini 998 back in 1985 used about 9L/100km and even more on a trip as it struggled to keep up with the speed limit, my wife's Skoda Octavia uses 7L/100km around town and goes down to 5L/100km on a trip. In 2000 excise taxes made up 44% of the government revenue, in 2013 39% due to better engines and with electric cars chances are it will keep dropping even more.

So yes it is a huge chuck of government revenue and somehow it will have to be collected, raising taxes on income is not popular and recently we have had some small tax cuts so the public expects cuts not increases.

I have noticed both my electricity bills and gas bills have gone up recently which I initially attributed to my son spending longer in the shower but I expect it is more taxes on the supply companies being passed on by higher prices to the end consumers. Maybe that is how it will be collected?

Years ago when we built the house we got gas cooking, gas heating and gas hot water. Now in my state (ACT) they want to end up 100% renewal energy so trying to phase out gas, I guess that is probably why the gas has gone up more than the electricity.

In summary for Australia
1, I don't expect petrol excise rates to be increased by the government - it was frozen in 2000 to shut up some whingers when the price went up significantly. But I do expect the price of crude to go down as demand is reduced, so possibly cheaper petrol for a while.
2, I don't expect personal income tax rate increases as that is too politically unacceptable. But I expect any cuts will be less than any increase due to people wages being higher so we will get bracket creep.
3, More taxes on energy supply companies so they put up their prices accordingly.