A cost-benefit analysis shows it makes sense to opt for a diesel car than a petrol version if your usage is high, says Prashant Mahesh. It seems everyone wants to buy a diesel car these days. Or at least they are thinking about it. Quite a natural reaction though, considering that petrol costs . 24 more than a litre of diesel (in Mumbai). The numbers speak for themselves. According to a Crisil Research report, the proportion of diesel cars in total cars sold will rise from the current 36% to 45% in 2015-16.