Many investors jumping on the Jamba Juice bandwagon are basing their optimism on a back-of-the-envelope calculation about the smoothie chain's financial prospects.

But much of the analysis is being extrapolated from nearly two-year-old unaudited financial statements that the San Francisco-based chain filed with California state regulators. Even using those dated figures, an argument can be made that the stock is fully priced.

It will probably be another week before Jamba Juice releases updated information about its recent earnings, as part of the company's proposed merger with the so-called blank-check company

Services Acquisition Corp.

The $358 million deal is being hailed by some as an innovative way for investors to get in on the ground floor of a company that has aspirations of doing for the blendered juice drink business what

Starbucks

(SBUX) - Get Report

did for coffee.

Without those figures, there's scant information available with which to analyze the privately held company. Management has kept mum. That silence is leaving a lot of room for speculative trading in shares of Services Acquisition, which are up about 49% to $11.10 since the deal was announced on March 13.

Several market professionals who have taken an interest in the Jamba Juice saga estimate that, on the basis of the company's unaudited financials, the company earned about $13 million on an operating basis in 2005. If that's the case, then on a fully diluted basis, Jamba Juice generated earnings about 20 cents a share. That calculation then translates into a price-to-earnings ratio of 58, which is comparable to the multiple that shares of Starbucks trade at.

Of course, Starbucks, with a considerably longer track record as a public company, dwarfs Jamba Juice on a market-capitalization basis. Starbucks has a current stock market value of $28 billion. On the basis of today's trading, Wall Street is giving Jamba Juice a market cap of about $726 million.

"I'm a big fan of Jamba, the concept and the product,'' says Robert Bexton, an analyst with Moirai Capital Management, a San Francisco hedge fund. "But the stock appears expensive where it is.''

Bexton's analysis has Jamba Juice earning between $13.5 million to $15.25 million on an operating basis in 2005. He says that on the basis of his numbers, the stock is pricey above $11. Bexton says he wants to see the 2005 financials before making a decision on whether to buy any shares.

To date, Jamba Juice has disclosed little about its 2005 performance. The company says annual sales at its 323 company-owned stores tallied $230 million last year. Sales at its 209 franchised locations were $115 million, of which Jamba Juice receives an unspecified percentage.

Jamba Juice also says it has had a "compound annual growth rate of 20% per year over the last three fiscal years.''

Clearly, many Jamba Juice fans are expecting some bigger numbers to come, given that the company's unaudited financial statements show that it grew rapidly from 2003 to 2004, when the company's fiscal year ended in June. The bulls are so impressed with Jamba's past growth that they don't appear troubled by the potential dilution to Services Acquisition's stock once the merger is completed and the company changes its name to Jamba Inc.

Right now, there are about 20.4 million shares of Services Acquisition outstanding. But soon after the deal closes, the number of outstanding shares could balloon to as much as 66 million, a problem

TheStreet.com

highlighted last week.

One thing the bulls point to is the 39% gain in company-owned store sales in 2005, up from the $166 million in 2004. Even better, they point out, is that since 2002, company-owned store sales are up 95%.

A good deal of the revenue gains are due to the fact that Jamba Juice, which opened in 1991, has expanded rapidly over the past four years. In 2002, Jamba Juice had 179 company stores and 169 franchised and licensed operations. Now it has 523 stores in 26 states.

Over that same stretch, earnings also have posted strong gains. In fiscal 2004, net profit totaled $7.98 million, up from $1.13 million in 2003. Operating earnings in 2004 were $8.39 million, up from $939,000 in 2003.

In 2004, Jamba Juice's operating margin -- operating income divided by revenue -- was 5.7%, roughly the same as in 2003, but up sharply from 2002's margin of 3.3%.

By comparison, Starbucks has an operating margin of about 11%.

The bottom line is that no one really knows where Jamba Juice's 2005 numbers will come out. Until then, anyone can call himself an expert but could still be proved an amateur.