This is a variation of Sanjoy Mahajan's The Art of Insight Section 1.4 (and problem 1.6)

How much oil does Australia import (in Barrels per Day)?

As in the text we approach this by estimating car consumption.

graph BT; Import[Oil imports Barrel/Day] ImportL[Oil imports L/Day] --> Import Barrel[Size of Barrel L] -->|-1| Import Consumption[Oil consumed L/Day] --> ImportL ImportRatio[Oil Imported / Consumed] --> ImportL CarConsumption[Oil Consumed by Cars L/Day] --> Consumption CarFraction[Oil Consumed in Total / Oil Consumed by Cars] --> Consumption Cars[Number of Cars] --> CarConsumption ConsumptionCar[Oil Consumed by Car L/Day] --> CarConsumption People[Number of People] --> Cars CarPeople[Number of Cars per Person] --> Cars

To estimate imports we estimate demand, since that is estimable. For oil, if we ignore reserves, then we have imports + production = consumption + exports. I don't know that Australia is a major oil exporter so I'll assume production and exports can be ignored. So then production is approximately consumption.

Estimating Car Consumption

A major use of oil is at petrol for consumer cars. Let's assume, as in the book, that car use is roughly equal to non-car use. So All Use/Car Use is 2.

There are 25 million people in Australia. It's a very car heavy nation; most people have a car. I'd guess there's around 0.8 cars per person (since this includes people who can't drive). This gives about 20 million cars.

A consumer probably fills up their car tank about once per week, for say a 40L tank. This means they use around 5L per day.

So the car overall consumption is about 100ML/day, or about 40 GL/year. This means the estimated overall consumption is about 200 ML/day.

Putting it together

A barrel is 160L, so 200 ML/day consumption is about 1.3 million barrels of oil per day. So our final estimate of imports is 1.3 million barrels per day.