Foursquare has started rolling out full-page ads on its mobile apps that will be served to members immediately after checking in at specific locations.

The new ad product joins promoted listings within the explore tab, which launched last July and enable business owners to promote specials to customers nearby.

According to AdAge, Captain Morgan is one of the first brands to try out the new check-in ads, using it to influence consumers immediately before making a purchase decision. Individuals at certain bars, nightclubs, or restaurants will be served an ad suggesting they order a “Captain and cola,” for example.

This campaign began on July 1st and is slated to run for four to six weeks. Captain Morgan’s parent company, Diageo, also plans on advertising its vodka brand Smirnoff through Foursquare check-in ads beginning in August. Another ad offers a coupon at Toys ‘R’ Us when shoppers check in to related locations, like a playground.

In an earlier interview, Foursquare chief revenue officer Steven Rosenblatt said that the company won’t allow brands to use post check-in ads for “conquesting” — allowing one brand to advertise to someone who checks in at a competitor’s location. Instead you will only be able to identify groups of consumers who share certain characteristics, such as frequenting coffee shops.

Foursquare has been incredibly careful about how it monetizes, launching only a select number of advertising offerings. Pricing for this ad unit is on a per-action basis, meaning brands are only charged when someone taps on the ad or saves it for later use.

Foursquare hasn’t commented on how much a post check-in campaign currently costs, or when more advertisers can get access to it.

[Via: AdAdge, Image credit: Thirteen of Clubs]