WOOLWORTHS is inviting marketers to be a fly on the supermarket wall - as long as they're prepared to pay for the privilege.

In recent weeks, brand owners have been invited to pay to access never-before-revealed data collected from the supermarket's 5.6 million Everyday Rewards Program cardholders.

Selling data to brand owners is opening up a potentially lucrative new revenue stream for the retailer. The data is proving to be of value to marketers, who are using it both to tailor marketing and expand the categories in which they operate.