Kevin, 39, a vice president at a Chicago Internet company, likes to spend money. During the six years he's been married, he's surprised his wife, Dawn, 37, by coming home with purchases—power tools, shoes, and even a Nissan Pathfinder—that he neglected to mention to her beforehand. "She was out of town and I just bought the new car and picked her up at the train station in it," he says.

Not telling your spouse that you've dropped tens of thousands of dollars on an SUV would be a source of terminal conflict in most marriages, but Kevin and Dawn have a secret that keeps his spending (and her thriftiness) from getting in the way of their marital bliss—they keep completely separate finances.

Kevin, who makes considerably more than Dawn, splits their $2,800 monthly mortgage payment evenly with his wife. They keep their own checking accounts, have their own credit cards, and save separately for the future. "She wasn't too thrilled about the car," Kevin says, "but I paid for it, so she didn't have too big of a problem."

Purchasing decisions—involving everything from toilet paper to a vacation home—are common flash points for spouses, and as the economy falters, discussions about them only become more fraught. "The No. 1 thing couples divorce over is money," says Leah Hanson, director of the Harmoney program, a Boston counseling service that teaches couples how to communicate about finances. "Recessions and rising prices result in divorce." To guard against that eventuality, many couples are becoming kitchen-table accountants who go fifty-fifty on every major bill and keep what's left for their own purposes.

Christian Farrell, a 33-year-old associate planning director at an advertising company, alternates weekly grocery duty with his wife, Rebecca, 32. They each write a check for half the rent on their Hoboken, New Jersey, apartment, and they keep track of the utility payments they make and settle up at the end of the month. Since they make similar money and have separate credit cards, the personal spending habits of one elicit little more than a shrug from the other.

"My wife likes spending on vacations and trips more than I do," Christian says. "But we don't fight about money, because most of the stuff we buy we individually control."

Kevin's experience has been similar. "With separate finances, not every little thing is scrutinized. There's less to argue about."

For some financially unyoked couples, dividing responsibilities is more complicated than making a fifty-fifty split. Marc Bliss, 40, a research-deployment manager for IBM in Knoxville, Tennessee, makes significantly less than his wife, Jerilyn, 40, a vice president of communications for a cable-television company. She brings in around 65 percent of the total household income, and so she pays 65 percent of the expenses.

"It doesn't make sense for us to split things evenly. We've used a percentage system for our entire six-year marriage, and we never really argue about money," Marc says.