Sequeira

"I don't think it's going to make a life-changing amount of money," says Mr. Sequeira.

Web's Hot New Commodity: Privacy Julia Angwin 2011

"Risk aversion was already huge because of what was happening in Europe, and it just increased due to the lack of visibility about what was going on in the Brazilian economy," said Carlos Sequeira , chief strategist for BTG Pactual, a Brazilian investment bank.

Growing Economies, Falling Markets Paulo Winterstein 2012

Mr. Sequeira has already received one payment of £5.56 $8.95 for letting Allow tell a credit-card company he is shopping for new plastic.

Web's Hot New Commodity: Privacy Julia Angwin 2011

Mr. Sequeira, the London real-estate executive, says that after he filled out an "intention" to get a new credit card, he received a £15.56 credit in his Allow account: a £10 signing fee plus a £5.56 payment from the sale of his data to a credit-card marketer.

Web's Hot New Commodity: Privacy Julia Angwin 2011

"I wouldn't give my car to a stranger" for free, Mr. Sequeira says, "So why do I do that with my personal data?"

Web's Hot New Commodity: Privacy Julia Angwin 2011

So in December, Mr. Sequeira became one of the first customers of London start-up Allow Ltd., which offers to sell people's personal information on their behalf, and give them 70% of the sale.

Web's Hot New Commodity: Privacy Julia Angwin 2011

Gareth Phillips for The Wall Street Journal Giles Sequeira now sells personal details about himself to advertisers.

Web's Hot New Commodity: Privacy Julia Angwin 2011

By comparison, Allow says it sells access to Mr. Sequeira for £5 to £10 per marketer.

Web's Hot New Commodity: Privacy Julia Angwin 2011

Testing the new privacy marketplace are people like Giles Sequeira, a London real-estate developer who recently began selling his own personal data.

Web's Hot New Commodity: Privacy Julia Angwin 2011

Allow, the company that paid Mr. Sequeira, is just one of nearly a dozen start-ups hoping to profit from the nascent privacy market.

Web's Hot New Commodity: Privacy Julia Angwin 2011