Middle Eastern oil producers are continuing to move substantial crude volumes through the Strait of Hormuz using low-visibility shuttle operations, helping to limit the impact of the Iran war on global oil prices despite persistent attacks on shipping.

People familiar with the shipments said the trade is operating at full capacity and carrying more than market estimates of 4 million barrels per day, although they did not provide a precise figure. Vessels crossing the strait often provide little information about their positions, making the flows difficult for traders and analysts to measure.

Before the conflict, approximately 20 million barrels per day passed through Hormuz, equivalent to about one-fifth of global oil supply. US Energy Secretary Chris Wright said 9 million barrels per day had crossed the waterway during the previous seven days, putting recent traffic at almost half the pre-war level and above many traders’ expectations.

The continued shipments have helped Brent crude futures remain largely within an $80-to-$90-per-barrel range during August. This is well below some early projections that oil could reach $150 per barrel if the conflict continued through the summer. Pipeline alternatives, releases from inventories and weaker global demand have also moderated the market impact.

Crude from the United Arab Emirates, Iraq, Qatar and Kuwait has been moved through Hormuz under shuttle arrangements, according to vessel-tracking information compiled by Bloomberg and data from Kpler and Vortexa. Cargoes are transferred outside the strait to tankers waiting in the Gulf of Oman.

Satellite data indicate that about 150 vessels, ranging from large tankers to bulk carriers, are now positioned off Oman, compared with roughly 40 in January. Many are reportedly waiting to receive cargo from vessels transiting Hormuz with their transponders switched off.

Abu Dhabi National Oil Co. said it remained committed to supplying customers despite attacks on its personnel, vessels and facilities. According to the company, 23 of its vessels have been attacked while crossing Hormuz since the conflict began, leaving one crew member dead and 20 injured. The company has sold about 135 million barrels of crude to international buyers and issued a further sales round.

People familiar with the crossings said some attacks and defensive actions have not been publicly reported. The trade has also been accompanied by seafarer casualties and a growing number of regional oil spills. A spill was visible in satellite imagery in the Gulf of Oman, although its source could not be identified.

Saudi Arabia has not yet used the shuttle system for large volumes of its own crude, but activity may be increasing as its alternative Red Sea route faces threats from Yemen’s Houthi militants. Two vessels loaded at Ras Tanura during the previous week, while Saudi tanker operator Bahri had 16 supertankers positioned off Oman and three more heading to the area. Together, those ships can carry 38 million barrels.

Insurers are also receiving a steady flow of business requests from Gulf producers. However, the limited willingness of shipowners to accept the security risks continues to constrain available tanker capacity and adds uncertainty to regional crude exports.