May 22 (Reuters) - Grades eased on Friday the last day of the volatile cash roll period and as investors worried that the U.S. and Iran would be unable to reach a peace agreement that would allow shipping traffic to return to normal in the Strait of Hormuz.

On the supply side, Baker Hughes said oil rigs rose by 10 to 425 this week, their highest since July 2025. However, U.S. oil operators in North Dakota are moving cautiously on ramping up drilling despite a sharp rise in oil prices driven by the Iran war, as companies wait to see if higher prices will last long enough to justify new investment, the state’s regulator said on Friday.

Meanwhile, prices to roll U.S. crude oil futures positions from June to July traded at $3.75 a barrel.

Traders use the three-day roll period to adjust their crude slates, square up positions and net out exposures following the expiration of the U.S. crude futures contract.

The spread between WTI and Brent/WTI widened for the first time in 10 sessions to last trade at minus $6.87 a barrel. It had touched the smallest discount in over a month this week.

In pipeline news, a line operated by Plains All American <PAA.O> ruptured in East Los Angeles, California, the company said on Friday, adding that the impacted section of the pipeline was shut down.

On the refining side, U.S. oil refiners are expected to have about 139,000 barrels per day of capacity offline in the week ending May 22, increasing available refining capacity by 516,000 bpd from the previous week, research company IIR Energy said on Friday.

• Light Louisiana Sweet for June delivery was unchanged at a midpoint of a parity and was seen bid and offered between a discount of 20 cents​​ and 20-cent a barrel premium to U.S. crude futures CLc1

• Mars Sour eased $1.50 at a midpoint of a $1.03 premium and was seen bid and offered between a 80-cent and $1.25 a barrel premium to U.S. crude futures CLc1

• WTI Midland eased 5 cents to a midpoint of a 30-cent discount and was seen bid and offered between a 50-cent and 10-cent a barrel discount to U.S. crude futures CLc1

• West Texas Sour was unchanged at a midpoint of a $4.8 discount and was seen bid and offered between a $5.00 and $4.60 a barrel discount to U.S. crude futures CLc1 ​

• WTI at East Houston, also known as MEH, traded between a 50-cent and 20-cent a barrel discount to U.S. crude futures CLc1

• ICE Brent July futures LCOc1 rose 96 cents to settle at $103.54 a barrel on Friday​.

• WTI July crude CLc1 futures rose 25 cents to settle at $96.6 a barrel on Friday​.

• The Brent/WTI spread widened 64 cents to last trade at minus $6.87, after hitting a high of minus $6.35 and a low of minus $7.15.