Many financial-services experts applaud the trend as investors are increasingly left on their own to manage their nest eggs. But others advise caution, saying that along with easy access to these sometimes-complex investment vehicles must come educational efforts and access to guidance.

From purchasing an annuity online to buying units of an annuity through a 401(k) plan via automatic payments, getting one of these insurance contracts -- which guarantee a steady stream of income -- has become almost as easy as buying a stock or a mutual fund.

And buying an annuity is likely to become even easier in coming months. Fidelity Investments has allowed customers since December to open a Fidelity Personal Retirement Annuity, a tax-deferred variable annuity, online. The company says that its online offering is one of the industry's first such tools and that it has had solid performance so far, though it declined to say how many contracts have been purchased. Fidelity also plans to make it possible for investors to purchase online an annuity with a guaranteed minimum withdrawal benefit.

Vanguard Group allows clients to fill out applications for annuities online, but they must then be printed, signed and mailed. Permitting clients to complete an annuity transaction online is something that the fund company will look into, though not in the short term, said Patti Colby of Vanguard's annuity and insurance services department.

TIAA-CREF will consider permitting clients to open annuities online "based on client demand and the medium's ability to help clients in a comprehensive way," spokesman Chad Peterson said.

In addition, insurers are increasingly offering annuities tailored specifically for 401(k) plans, some of which permit an investor to dollar-cost average into an annuity by making small purchases over a long period of time, just as they purchase mutual funds.

Moshe Milevsky, a finance professor at Toronto's York University, said he is bullish on the trend.

"If you can buy your mutual funds online, and if you can buy complicated exotic options online and you can buy and sell currencies online, why can't you do it with an annuity?" Mr. Milevsky said. "Some of these things are infinitely more complex than a basic garden-variety annuity."

Those who are comfortable making the transaction online shouldn't be forced to go to an intermediary, he said. "The cheaper we can make it for them, the better."

Some caution that the process of purchasing annuities -- some of which can be extraordinarily complex and have been criticized for high fees and suitability issues -- must come with proper support and checks. It is important, for example, to ensure that an annuity contract is suitable for an investor no matter how it is being purchased, they say.

"I think it's an awful idea to buy an annuity online," said Matthew Tuttle, a financial planner in Stamford, Conn. Annuities have "many complexities and moving parts," so investors may need help making decisions.

"Ease of getting the things is great as long as it's combined with education," Mr. Tuttle said. "I think it's dangerous if no one can explain to me what this is. You need to know what you're getting and how it fits in with what you're already doing."

He noted that annuity purchasers face some complex decisions, and that in many cases it pays to shop around for the best rate. "If I'm married, can I get the best price by purchasing an annuity just for my lifetime?" he said. "If I die in a year, my wife gets nothing. It really helps to have someone sitting there explaining that to you."

Fidelity's online application evaluates the suitability of an annuity to a particular customer with a few questions about the customer's existing annuities, financial situation and risk tolerance.

Mr. Milevsky said good business practice dictates that next to the online annuity application there be a "very big 'Click Here, and you will be connected to customer support.'" In addition, he said, educational information should be available online.

Fidelity offers online educational materials and videos on annuities, and an 800 number that for more customer support is displayed prominently throughout the annuity application process.

Fidelity Personal Retirement Annuity is a very simple annuity without complicated riders, and clients may choose to create their own portfolio of investments or to have Fidelity manage their investment options, said Joan Bloom, senior vice president of marketing and product management in Fidelity Investments Life Insurance Co. Still, to some clients it "can appear to be a little bit complex" because it has suitability requirements, so Fidelity offers the option to save their online application at any point and request the help of a representative.

Write to Daisy Maxey at daisy.maxey@dowjones.com

By DAISY MAXEY -March 11, 2008; Wall Street Journal , Page D4