UPDATE 1-TGS-Nopec's strong Q3 lifts shares, outlook cloudy

* TGS-Nopec posts above-forecast 55 pct jump in Q3 EBIT

* Shares up 9.9 pct in early trade

* Says global turmoil likely to affect future growth

* Revises up 2008 revenue and investment targets

* Says Q4 visibility typically low due to late data sales

(Adds details, quotes, shares)

OSLO, Oct 30 (Reuters) - Norwegian seismic surveyor TGS-Nopec (TGS.OL) posted a bigger-than-expected rise in third quarter operating profit, lifting its shares, though the company said its outlook was clouded by global market turmoil.

Earnings before interest and tax rose to $76 million in July-September from $49 million a year earlier and above the $66 million average forecast in a Reuters poll of nine analysts.

Revenues surged 71 percent to $171 million, a new quarterly record, led by strong sales in Europe and the Gulf of Mexico.

"Our performance remains well ahead of our expectations so far this year," Chief Executive Hank Hamilton said.

"Although the current global financial situation creates uncertainty in our industry, our record backlog and highly flexible business model uniquely position us to take advantage of new opportunities," he added.

TGS-Nopec said the financial market turmoil was "likely to have an impact on future growth", adding that "based on recent offers from suppliers, rates for contracting seismic vessels have clearly peaked and availability seems to be improving".

Shares in TGS-Nopec were up 9.9 percent to 33.30 crowns at 0828 GMT, outpacing a 3.6 percent rise in Oslo's index .OSEBX.

TGS's core business is conducting and selling non-exclusive seismic surveys, which help oil and gas producers share the risks and costs of exploring for new resources.

The segment has been hit harder by lower oil prices and market turmoil than the market for higher-tech surveys for single clients, analysts said.

TGS-Nopec raised its 2008 revenue target by $10 million to $560-590 million and its multi-client data library investments by $25 million to $275-300 million as prefunding for such non-exclusive scans from oil and gas companies dries up.

"Revenues are well ahead of plan for the first nine months of 2008," it said, but warned of low visibility in non-exclusive sales from the data library in the fourth quarter.

"In all previous years, the fourth quarter has been TGS's highest revenue quarter, as this is traditionally the peak season for late sales of library data. These late sales have low forward visibility and are notoriously difficult to forecast."

Late sales are sales of existing data from the library, as opposed to sales of newly acquired survey data. (Reporting by Wojciech Moskwa and Joergen Frich; Editing by Will Waterman)