* Q3 sales up 29.5% at 126.5 mln pounds, margins stable
* Sees no reason why strong sales growth should diminish
* Says analyst consensus is for group to make profit in 2011
* Shares down 3.7 percent
(Adds company, analyst comments, shares, detail, background)
By Mark Potter
LONDON, Sept 7 (Reuters) - Sales at British online grocer Ocado jumped nearly 30 percent in the latest quarter, the recently listed company reported on Tuesday, but gave few new clues about when it expects to turn a profit.
Ocado, which sells the products of upmarket grocer Waitrose , posted a 29.5 percent rise in third-quarter sales and said it saw no reason why this pace should slow.
Chief Executive Tim Steiner noted that most analysts expect the group will make a profit next year.
However, some analysts remained concerned about how quickly earnings would build, particularly as Ocado is planning a big investment in a new warehouse.
"Given that the group has to engage in material capital investment to sustain its sales growth and has yet to demonstrate profitability on an already considerable sales base, we continue to harbour reservations about the valuation of Ocado," said Shore Capital analyst Clive Black.
At 0825 GMT Ocado's shares were down 3.7 percent at 151.25 pence.
The company, founded by three former Goldman Sachs bankers in 2000, cut the price of its July initial public offering (IPO) by almost a quarter to attract investors, and the stock has fallen as much as 27 percent since listing at 180 pence.
COMPETITION
While Britain's store groups are struggling in an uncertain economic recovery, internet retailers are booming as time-pressed shoppers flock to buy goods online.
However, some analysts are unsure whether Ocado's model of distributing from a central depot will ever be as cost-effective as filling online orders from local stores, as rival supermarkets do.
The group also faces growing competition, with Waitrose stepping up its own online service and analysts suggesting Wm Morrison Supermarkets, Britain's fourth-biggest grocer, may unveil a plan to move online in a strategy update on Thursday.
Finance Director Andrew Bracey said he welcomed competition.
"Once you get general adoption of a type of service ... you tend to see an acceleration in that service overall," he told reporters on a conference call.
"We're already happily competing with the largest and best operators in the grocery world," he added, referring to competitors like Tesco and Asda.
Bracey was also confident that Ocado's strong sales growth would continue.
"We can't see any particular reason why that's going to diminish," he said.
While annualising the start of the group's Sunday trading might slow growth a little, Ocado has high hopes for the expansion of its own-label range, Bracey said.
Gross sales rose 29.5 percent to 126.5 million pounds ($194 million) in the 12 weeks to Aug. 8, in line with growth in the first half of its financial year.
Gross profit margins were stable versus the first half.
Steiner said Ocado was making progress with talks to build a second depot, which it hopes to open in 2012, and this was his focus rather than short-term movements in the shares.
"I'm very focused on where it (the stock) will be trading in two or three years time, not where it will be trading at lunchtime," he said. ($1=0.6511 pounds) (Editing by Greg Mahlich)