Costco is traditionally a few pence cheaper than supermarkets. RAC who undertake fuel watch have been saying for sometime retailers are overcharging.
https://www.bbc.co.uk/news/business-67254013
But let's do some maths. Wholesale price for 22nd Nov'23 was 101.34p
Lets add VAT which is 20% - 20.268p
And Distribution costs - 2p/l
Retailer 'profit' were traditionally 4-8p/l. All adds up to around 130p.
It doesn't take a genius to work out the difference. If you go back along the RAC chart to find to find prices over the last few years for similar wholesale prices and then look at retail price, pump prices are significantly higher today. So I'll stand by my original comment, motorists are being fleeced and overcharged by "everybody else".