The Saudi bourse regulator has ordered six investors to pay a total 278.1 million riyals ($74.16 million) for trading violations, it said in a statement on Saturday.

Like others in the Gulf region, Saudi Arabia's stock exchange has been dogged by allegations of being opaque and subject to manipulation of stock prices, and the regulator has slapped hefty fines on investors and executives found guilty of violations.

An appeals panel of the Capital Market Authority issued a final ruling in the case of the six men found guilty of violating trading regulations in transactions with shares in Tihama Advertising and Public Relations Co <4070.SE> in 2006, the CMA said in the statement on the bourse website.

One of the investors was fined 200,000 riyals and ordered to pay back 142.8 million riyals which CMA said were gains he made in these transactions.

The appeal panel also banned four of the six investors from trading in shares of listed firms or working for such companies for three years.

An official at Tihama, Ibrahim Esmail, could not immediately be reached for comment.

The Saudi bourse is gradually opening up to direct foreign ownership amid tough competition from regional bourses.

Over the past two years, CMA has stepped up efforts to clamp down on irregularities, imposing hefty fines and one jail sentence and revoking the licenses of several brokerage firms for violating market laws and regulations.

(Reporting by Souhail Karam; editing by Firouz Sedarat)