SINGAPORE, April 17 (Reuters) - Spot differentials for fuel oil retreated on Thursday, with trading momentum thinning ahead of a holiday.

Singapore cash differential for very low sulphur fuel oil (VLSFO) dipped backed to around a premium of $3 a metric ton over Singapore quotes, reflecting slightly softer offers.

Margins for VLSFO LFO05SGBRTCMc1 continued to hover below premiums of $9 a barrel, based on LSEG data.

Meanwhile, cash differential for 380-cst high sulphur fuel oil (HSFO) ended the week in steeper discounts, though cracks FO380BRTCKMc1 held stable near premiums of $1 a barrel on Thursday.

In spot tenders, Vietnam's Nghi Son this week offered more fuel oil for April loading. FUEL/TENDA

As for derivative markets, trading was also broadly quiet for key fuel oil contracts, market sources said. Backwardation spreads narrowed at the prompt months for both HSFO and VLSFO.

REFINERY UPDATES

- Valero Energy Corp said it was taking a $1.1 billion pre-tax impairment related to its California refineries and told state regulators it would permanently shut or restructure its San Francisco-area refinery in Benicia, California by the end of April 2026.

- Motiva Enterprises has restarted the gasoline-producing fluidic catalytic cracker at its 626,000 barrel-per-day (bpd) Port Arthur, Texas refinery, people familiar with plant operations said.

OTHER NEWS

- Oil prices extended gains on Thursday on the prospect of tighter supply after Washington imposed further sanctions to curb Iranian oil trade and as some OPEC producers pledged more output cuts to compensate for pumping above agreed quotas. O/R

- Turkey's largest oil refiner Tupras has returned to buying Russian Urals crude cargoes, after it stopped doing so earlier this year due to stronger U.S. sanctions on Moscow, according to three trading sources and shipping data.

- The Organization of the Petroleum Exporting Countries (OPEC) has received updated plans for Iraq, Kazakhstan and other countries to make further cuts to oil output, to compensate for pumping above agreed quotas, the group said.

- The United States issued new sanctions targeting Iran's oil exports, including against a China-based "teapot" oil refinery, as President Donald Trump's administration seeks to ramp up pressure on Tehran.

WINDOW TRADES O/AS

- 180-cst HSFO: No trade

- 380-cst HSFO: No trade

- 0.5% VLSFO: No trade

ASSESSMENTS

(Reporting by Jeslyn Lerh;; Editing by Rashmi Aich)

((jeslyn.lerh@thomsonreuters.com))