I went to SPC and pump petrol last Sat besides the usual 6% display outside the kiosk and the SPC & U card discount ranging (5-7%) there is another 8% discount inside the kiosk.
In total I get 25% discount
from the breakdown below:
a) 6% station discount
b) 6% on SPC & U card discount
c) 8% discount given inside SPC while making payment.
d) 5% paid via Citibank Divided Credit Card More discount if you pay by Citibank Dividend Card 5% so total can reach as high as 25% overall
Not sure how long the 8% will last, maybe they try to avoid a price war with the others so they discreetly display inside.
Click link below for comparison with others
http://www.petrolwatch.com.sg/priceguru.php 
