Five hundred Google. Six hundred Google. Seven hundred Google.

Are we going to see $1,000 Google ( GOOG)?

Why not? After all, isn't the sky the limit? Sandeep Aggarwal, an analyst at Oppenheimer & Co., just raised his price target for the stock yesterday to $850. So I figure I'd go to four figures.

And Wall Street always likes a big round number. Dow 10,000. Nasdaq 5,000, oil $100.

Google hit a new record of $736 yesterday. It's been gaining an average of about $5 a day since it started taking off two months ago. By my calendar, it's on track to hit the big $1,000 in the last week in January. You want to take the over or the under?

If everyone piles on, it could of course get there much sooner. A self-fulfilling prophecy.

So what would $1,000 Google look like?

That stock price would give this nine-year old company a market value of around $310 billion. That's still smaller than the likes of Exxon ( XOM), at $486 billion, and General Electric ( GE) at $412 billion. And it's still slightly behind Microsoft ( MSFT) at $344 billion.

But at $1,000 a share, Google would be worth more than veteran drug giants Merck ( MRK) and Pfizer ( PFE) together. It would be worth twice as much as Apple ( AAPL).

That's some baby.

But the company's soaring stock market fortune raises one big question: What sort of long-term return can the shares offer from these levels?

OK, at these prices, its valuation wouldn't even look that crazy. Analysts forecast earnings of about $15.57 a share this year and $20.66 next. So at $1,000, Google would be on a forward price-to-earnings ratio of 48.

Steep? Sure. Other companies of that size are more often on price-to-earnings ratios of 12, 15, or maybe at a stretch, 18 -- the valuation you'd expect from a mature business.

Granted, Google should command more. Maybe even a lot more. It's growing fast. And, like Apple, it has one extra competitive advantage: Third-rate competition.

So no, $1,000 Google isn't crazy. It could happen. But right now the stock is a "mere" $735.

Sure, it has big momentum. Lots of traders are piling in so they don't get left behind. And many investors doubtless have high hopes. But check it out -- are you hoping the shares will produce an annualized investment return of, say, 20% a year from here?

If so, that would make Google shares $4,500 apiece in 10 years' time. The company's market value then: $1.48 trillion.

That's three Exxons.

Jumbo companies, by definition, are usually pretty mature. But let's be charitable and imagine Google, at $4,500, would still command an impressive 20 times forward earnings.

To get there, earnings would have to grow at a compound rate of 30% a year for 10 years. That is a stunning rate of growth to sustain for an entire decade.

And it would send net income to $70 billion -- or 75% more than Exxon Mobil is managing to make today.

Possible? Sure. Likely? We'll see.

Yet this is what has to happen if Google is going to return 20% a year from these levels.

And less heroic assumptions take their toll on the numbers. Imagine the earnings grow by a more modest 20% a year over this period. That's still a pretty remarkable compound growth rate for a decade. Imagine, furthermore, that the stock ends up in 10 years' time on 18 times forecast earnings, in line with recent market averages.

In that scenario, your shares will have only made you about 9% a year.

Nine percent.

Sure, it's a decent return. Risk-adjusted? Maybe not. If long-term earnings growth is just 15% a year, the shares are only going to make 6%.

Everything profitable has a value. And that value, alas, is always a finite number.

Meanwhile, the bulls are in charge and animal spirits are roaring. So who dares talk in terms of limits?

Next week: "Google $2,000!"

(Do I really mean $2,000 factorial? Maybe. Why not?)
In keeping with TSC's editorial policy, Brett Arends doesn't own or short individual stocks. He also doesn't invest in hedge funds or other private investment partnerships. Arends takes a critical look inside mutual funds and the personal finance industry in a twice-weekly column that ranges from investment advice for the general reader to the industry's latest scoop. Prior to joining TheStreet.com in 2006, he worked for more than two years at the Boston Herald, where he revived the paper's well-known 'On State Street' finance column and was part of a team that won two SABEW awards in 2005. He had previously written for the Daily Telegraph and Daily Mail newspapers in London, the magazine Private Eye, and for Global Agenda, the official magazine of the World Economic Summit in Davos, Switzerland. Arends has also written a book on sports 'futures' betting.

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