US Cash Crude-Grades mixed on first full day of roll trade

March 21 (Reuters) - U.S. crude oil differentials were mixed on Friday, the first full day of the cash roll period that traders use to square their positions, brokers said.

The roll trade period, which traders use to adjust slates, began on Thursday afternoon and will continue for three full days. Trading tends to be more volatile during the roll period.

The cash roll for April to May traded at 35 cents.

U.S. energy firms this week added oil and natural gas rigs for the first time in three weeks, energy services firm Baker Hughes BKR.O said in its closely followed report on Friday.

The oil and gas rig count, an early indicator of future output, rose by one to 593 in the week to March 21. Oil rigs fell by one to 486 this week, while gas rigs rose by two to 102.

Light Louisiana Sweet WTC-LLS for April delivery rose 30 cents to a midpoint of a $2.50 premium and was seen bid and offered between a $2.15 and $2.85 a barrel premium to U.S. crude futures CLc1

Mars Sour WTC-MRS eased 5 cents to midpoint of an 85-cent premium and was seen bid and offered between a 75-cent and 95-cent a barrel premium to U.S. crude futures CLc1

WTI Midland WTC-WTM was steady at a midpoint of a $1 premium and was seen bid and offered between an 80-cent and $1.20 a barrel premium to U.S. crude futures CLc1

West Texas Sour WTC-WTS fell 30 cents to a midpoint of parity and was seen bid and offered between a discount of 10 cents and a 10-cent a barrel premium to U.S. crude futures CLc1

WTI at East Houston WTC-MEH, also known as MEH, traded between a $1.35 and $1.55 a barrel premium to U.S. crude futures CLc1

ICE Brent May futures LCOc1 rose 16 cents to settle at $72.16 a barrel

WTI May crude CLc1 futures rose 21 cents to settle at $68.28 a barrel

The Brent/WTI spread WTCLc1-LCOc1 narrowed 6 cents to last trade at minus $3.87, after hitting a high of minus $3.78 and a low of minus $3.90