OSLO - U.S. oil company ExxonMobil said it may sell its 9.4 percent stake in Gassled, the owner of Norway's gas transport system, but has no plans to reduce its activities on the Norwegian shelf.

Gassled is a joint venture between oil and gas companies on the Norwegian continental shelf which owns the integrated North Sea gas transport system carrying nearly 100 billion cubic metres of Norwegian gas per year to Europe.

We are continuously looking at optimising our portfolio and this time we are marketing Gassled to see if we can sell it, Exxon Norway spokeswoman Kristin Kragseth said on Tuesday.

The decision to market the stake comes a year after Exxon, as well as other foreign minority Gassled owners including Total, Shell, ConocoPhillips and Eni, accused the Norwegian government of giving too much sway over Gassled to companies it has influence over.

More than 70 percent of Gassled is controlled by state-owned Petoro and majority state-owned Statoil, which the foreign companies said made it tough for them to have influence over strategic decisions on pipelines and access to new fields.

Unlike many other oil- and gas-rich countries which have succumbed to resource nationalism, Norway prides itself on equal treatment of all market participants.

Nevertheless, the 2007 tie-up between the oil and gas divisions of its two biggest producers, Statoil and Norsk Hydro, left the bulk of the Norwegian shelf's production under control of a single company, which is two-thirds owned by the state.

Exxon says it is the second-largest producer in Norway after Statoil, with output of about 400,000 barrels of oil equivalent per day, which amounts to about 10 percent of the Norwegian shelf's total production and ExxonMobil's worldwide output.

We don't intend to reduce our level of activity in Norway at all. In fact we will be doing 3D seismic (scans for potential oil and gas deposits) in the Norwegian sea next year, she said.

In operation since 2003, Gassled has no employees and is organised through committees. It has set up a different company, Gassco, to run the 7,800 km (4,847 miles) gas pipeline system, some platforms and onshore facilities on behalf of the owners.

In 2008, Gassco had gross tariffs of 26.6 billion Norwegian crowns ($4.59 billion) and operating costs of 5.2 billion.

According to Gassco's website, Gasco owners are: Petoro (38.459 pct), Statoil (32.102), ExxonMobil (9.428), Total (7.783), Shell (5.319), Norsea Gas (2.726), ConocoPhillips (1.996), Eni (1.525) and DONG Energy [DOENRY.UL] (0.662). (Editing by Sue Thomas)