DUBAI, Sept 4 (Reuters) - Oman's OQ Gas Networks (OQGN), the pipelines business of state oil giant OQ, said on Monday it plans to float up to 49% of its shares, in what is expected to be the biggest initial public offering in the Sultanate in almost two decades.

The offering, which begins this month, will provide investors with access to growth in the company that holds a natural monopoly over essential gas transportation in the country, the company said in a statement.

OQGN is Oman's exclusive gas transportation system operator, supplying natural gas to the country's power plants, freezones, industrial clusters, LNG complexes and other customers.

The IPO could raise between $700 million and $800 million, a source with knowledge of the matter told Reuters, which would make it the largest since Oman Telecommunications raised 288 million rials ($748.09 million) through the sale of a 30% stake in 2005.

OQGN did not immediately respond to a request for comment on the size of the IPO.

Reuters first reported the IPO plans for the company last May.

($1 = 0.3850 Omani rials) (Reporting by Hadeel Al Sayegh, Editing by Louise Heavens and Sharon Singleton)