DUBAI, May 13 (Reuters) - Saudi Arabia's stock market regulator said on Wednesday it had approved an initial public offer of shares in Arabian Contracting Services Co, an advertising firm, the fourth flotation in the kingdom this year.

The Capital Market Authority (CMA) said Arabian Contracting Services Co would offer investors 16.5 million shares representing 30 percent of its capital, and some of those shares would be offered to institutional investors.

The offer will run between June 10 and 16; the regulator provided no other details and did not say what the company's business was.

The flotation will follow the already completed public placements of Middle East Paper Co (MEPCO) and Saudi Company for Tools and Hardware (SACO) . Also, last week the CMA approved a planned offer by Saudi Ground Services Co .

Although Saudi Arabia's stock market has been volatile in the last few months because of oil's plunge late last year, newly listed shares - which are usually sold to local investors at a discount - remain in demand.

MEPCO, which listed earlier this month, soared as much as 71 percent before stabilising, and SACO has surged its daily 10 percent limit for two sessions in a row after listing on Tuesday.

Saudi Arabia will open its stock market to the first wave of qualified foreign investors on June 15 and the regulator has said that access to IPOs for foreigners may be possible, but will be decided on a case-by-case basis.

(Reporting by Olzhas Auyezov; Additional reporting by Marwa Rashad in Riyadh; Editing by Andrew Torchia) ((olzhas.auyezov@thomsonreuters.com; +971 56 225 4871; Reuters Messaging: olzhas.auyezov.thomsonreuters.com@reuters.net))

Keywords: ARABIAN CONTRACTING SERVICES IPO/