The source reports that: "Petrol Index is an annual ranking of the relation between petrol prices and salaries conducted by Picodi.com since 2019."
According to the source the methodology is: "In this study, the source used the latest average wage data published by national statistics offices or relevant ministries. In countries where such data is not published, we used statistics from Numbeo. The average petrol prices in 104 countries in the first half of 2023 were taken from GlobalPetrolPrices.com and other local sources. The difference between prices in June and January was calculated in local currencies. In order to calculate the “Petrol Index”, we divided the average net wage (obtained through local wage calculators) by an average price of a litre of petrol in June. For currency conversion, we used the average exchange rate data from Google Finance for June 2023."