UPDATE 2-Australia's Nexus shares soar on Shell takeover talk

* Biggest shareholders approached on possible takeover -report

* Nexus said no takeover approach received

* Shares trim gains after jumping 30 pct to 9-mth high

* Stock's volume on Tuesday exceeds 90-day avg by 12 times (Recasts; adds comment from Nexus, Shell and analyst)

By Fayen Wong

PERTH, Aug 3 (Reuters) - Shares of Australian oil and gas company Nexus Energy (NXS.AX: Quote) surged as much as 30 percent on Tuesday on speculation Royal Dutch Shell (RDSa.L: Quote) was lining up an A$480 million ($438 million) takeover offer to secure gas supplies for its flagship floating LNG project.

Nexus shares later cut their gains after the firm denied that it had received any approaches. Shell declined to comment on market speculation, but said gas from the Crux field owned by Nexus was an "integral part" of its Prelude floating Liquefied Natual Gas (LNG) project in western Australia.

The Australian newspaper reported that some of Nexus' top shareholders had been sounded out about a possible 50 cents per share bid, stoking speculation that Shell may be interested in making an offer for Nexus.

The largest shareholder of Nexus is Viking Shipping Ltd which owns 7.2 percent of the stock. U.K. fund manager M&G Investment Management holds 6.25 percent of Nexus, while Nexus' non-executive director Symon Drake-Brockman owns 4.9 percent.