Normally $41.99, I find this stuff to be pretty good, though maybe only really worth buying in special. Good for petrol or diesel is detergent based, no hydrocarbons.
Marketing spiel below:
Australian made, Fuel Doctor Fuel Conditioner. Fuel Doctor has been formulated to clean and disperse gums, varnish, condensation, microbial and biological growths while also improving fuel delivery and combustion performance; Increasing fuel economy and minimising harmful emissions. Fuel Doctor also provides upper cylinder lubrication qualities and with ongoing use will help prevent fuel and Diesel Particulate Filter (DPF) blockages. Fuel Doctor is suitable to use in all petrol and diesel engines and will stabilise and extend fuel life for up to 24 months
Lots of good reviews. May be worth a shot on older cars with bad km's/tank efficiency!