Someone asked me on Facebook if the Fiesta ST required premium fuel. So, I decided to get a definitive answer. The short answer is that the car does NOT need premium fuel. The Fiesta ST will run just fine on 87 octane fuel. The ECU will compensate and make the necessary adjustments. However, the car will (of course) perform better with higher grade fuel. Here's an interesting breakdown of HP/TQ figures based on octane rating. We know that the advertised numbers, on 93-octane are: 197HP/202TQ. Also, keep this in mind, you should get slightly better fuel economy with 93-octane… all things being equal. But, how much do you give up by using 87-octane fuel? Here is some info that I think you will only find first here on Fiesta ST Network. The engine calibration will reduce those numbers to: 174HP/189TQ.