With my UOB One card, I'm able to enjoy 5% cash rebate and 2% smart cash. If you apply for the eCard, you can get 1 point for every RM you spend. So, in total, I get 7.8% rebate each time I pumped at BHPetrol with UOB One card and eCard. You can see the comparison of reward system for each petrol station here.
The eCard can be applied at the petrol station but you're not able to get it on the spot. The petrol station will send the application form to HQ to process. After 2~3 weeks, HQ will send out the card to your mailing address.