Coles shoppers are paying a hefty premium on some groceries when they shop online and use the supermarket's supposedly free "click and collect" service or home delivery.

Fairfax Media compared in-store and online prices on 10 popular brand label items at Coles and found eight of them were 10 per cent more expensive for online shoppers.

Coles charges between $4 and $14 to deliver orders under $150 in metropolitan areas, depending on when the customer is available to receive it.

Online orders can also be collected from some stores using its "click and collect" service, which it advertises as being free.