—by Charlotte Cavaretta, account supervisor and social media strategist, MSLGROUP in New York

Brands around the world are putting money and resources into engaging their fans online. Yet some are going even further by turning Facebook into a sales engine. In the past few weeks we’ve seen several stories about brands—ranging from Heinz Ketchup to Oscar de la Renta—which are offering products to their Facebook fans exclusively through their branded Facebook pages.

Starting today, Heinz Ketchup will be selling Heinz Tomato Ketchup Blended with Balsamic Vinegar, a limited edition, exclusively on its Facebook page until the product begins to appear in supermarkets in late December. The retail price is $2.49. People who order it through Facebook will have to pay an $2 for shipping and handling.

“We’re starting on Facebook first for our most avid fans,” said Noel Geoffroy, the vice president for United States retail brands at H. J. Heinz, in an interview with The New York Times.

By offering its tried-and-true fans an exclusive first, the brand is not only providing them an award—it is also enabling passionate customers to spread the word about the offer and increase purchase intent.

This month, Oscar de la Renta is selling a cocktail-sized, flower-shaped perfume ring exclusively on its Facebook page. The $65 ring contains a solid concentration of L’Esprit d’Oscar, the brand’s first fragrance in 10 years. The fashion house launched the perfume in April, giving away free samples to people who liked its Facebook page, according to The Daily Mail.

In an interview with Mashable in September, Oscar de la Renta CEO Alex Bolen said he expects Facebook “will become a major channel of commerce” for many brands. “Whether [Facebook] becomes one of ours depends on us developing products that are right for our brand and that channel of our commerce,” he said in the interview.

For our part, we have certainly noticed the brand’s popularity on social networks, and we are quite impressed that @oscarPRGirl has nearly 92,000 Twitter followers, while the Facebook page has some 244,000 fans.

These aren’t the first brands to experiment with Facebook commerce and they surely won’t be the last. Numerous brands and retailers have created shopping tabs on their Facebook pages allowing consumers to browse and make purchase without leaving Facebook. But as we can see, it is the unique selling proposition–the exclusivity–that appears to generate the most buzz.

With more than 800 million active users, Facebook is providing brands with a new and exciting opportunity to drive sales. What do you think: Will brands find the sweet spot of share of voice AND share of wallet?